Forensic Chemistry Definition of Terms
Absorbance - The measure of concentration of material present; the negative log (base 10) of transmittance [–log 1/T ] of product of extinction coefficient, path length, and concentration, written as
A = Ebc.
Absorption - The incorporation of liquids or gases into the body. Absorption is also the process by which liquid hazardous materials are soaked up by sand, sawdust, or other material to limit the spread of contamination. A mechanical phenomenon wherein one substance penetrates into the inner structure of another, as in absorbent cotton or a sponge. An optical phenomenon wherein atoms or molecules block or attenuate the transmission of a beam of electromagnetic radiation.
Absorption band - A region of the absorption spectrum in which the absorbance passes through a maximum point.
Absorption elution - An improved, direct way of showing the presence of agglutinogens.In this method, antigenic material is first allowed to come in contact with antisera. The homologous antibody is specifically absorbed by a given agglutinogen.
Absorption inhibition - A classical, indirect way of demonstrating the presence of an agglutinogen. This method involves the addition of a tittered antiserum to the bloodstain.
Absorption spectrum - A plot, or other representation of absorbance, or any function of absorbance, against wavelength, or any function of wavelength.
Absorptivity - (a) Absorbance divided by the product of the sample pathlength. (b) and the concentration of the absorbing substance
(c) a = A/bc
Acetaldehyde (CH3CHO) - A colorless liquid having a pungent and fruity odor; highly flammable and toxic, used chiefly to manufacture acetic acid. The first product of ethanol metabolism. Also known as
Acetate - A salt or ester of acetic acid. A manufactured fiber in which the fiberforming substance is called cellulose acetate. Where not less
than 92% of the hydroxyl groups are acetylated, the term triacetate may be used as a generic description of the fiber.
Acetone - The simplest ketone. A solvent for gunpowder. A highly flammable, water-soluble solvent.
Acid phosphatase - An enzyme found in high concentration in seminal fluid.Any nonspecific phosphatase requiring an acid medium for optimum
Acid phosphatase test - One of the most published and most widely employed techniques for semen identification. This enzyme can be found in the male prostate gland and is sometimes abbreviated as AP.
Acid phosphatase in human seminal fluid originates from the prostate gland (often referred to as prostatic acid phosphatase ).
Acoustic coupler - A device used to attach a modem to the telephone system by placing the telephone handset on a set of rubber cups.
Acrylamide monomer - Produced by the reduction of acrylonitrile by either liquid ammonia or by calcium bisulfite.Produced by the reduction of acrylonitrile by either liquid ammonia or by calcium bisulfite.
Acrylic fiber - Generic name for a manufactured fiber in which the fiber-forming substance is any long-chain synthetic polymer composed of at least 85% by weight of acrylonitrile units.
Actinic rays - Light rays of short wavelengths occurring in the violet and ultraviolet parts of the spectrum, which produce chemical changes, as in photography.
Activation - The heating of the adsorbent layer on a plate to dry out the moisture and maximize its attraction and retention power.
Active decay - That phase of corpse decomposition that follows bloat, is characterized by much maggot activity, and terminates with a rapid decrease in body weight.
Activity node - An individual’s past and present homes, current and previous work sites, and residences of partners, friends, and family members.
Acute - Severe, usually crucial, often dangerous in which relatively rapid changes are occurring. Acute exposure runs a comparatively short course.
Acute effect - A pathologic process caused by a single substantial exposure.
Acute exposure - A single encounter to toxic concentrations of a hazardous material or multiple encounters over a short period of time (usually 24 hours).
ADA (adenosine deaminase) - An enzyme found in the serum of blood.
Adaptation - The tendency of certain receptors to become less responsive or cease to respond to repeated or continued stimuli.
Adenine - (A) A nucleic acid consisting of a chemically linked sequence of subunits. Each subunit contains a nitrogenous base, a pentose sugar, and a phosphate group. One of the four building blocks of DNA. In the DNA molecule adenine forms a chemical bond with thymine.
Adenosine triphosphate (ATP) - A nucleoside triphosphate that upon hydrolysis results in energy availability for processes such as muscle contraction and synthesis of macromolecules, including protein and carbohydrates.
Adsorbent - The stationary phase for adsorption thin-layer chromatography. A solid or liquid that adsorbs other substances, e.g., charcoal, silica, metals, water, and mercury.
Adsorption - (1) The action of a body, such as charcoal, in condensing and holding a gas or soluble substance upon its surface.
(2) The adherence of
atoms, ions, or molecules of a gas or liquid to the surface of another
substance. (3) Finely divided or microporous materials having a large
active surface area are strong adsorbents.
(4) The attraction between the surface atoms of a solid and an external molecule by intermolecular forces.
Advanced Chemiluminescent Enhancement System - Used for
the nonradioactive quantitation of small amounts of human DNA.
Agar - A polysaccharide extracted from seaweed. A gelatinous product extracted from certain red algae used chiefly as a gelling agent in culture media.
Agarose - The neutral gelling fraction of agar commonly used in gel electrophoresis.
Agglutination - The clumping together of living cells as a result of a reaction between the cells and an appropriate immune serum.
Agglutinin - A chemical product of the process of immunization arising in blood serum and causing the red corpuscles, with which it is brought into contact, to coalesce into floccules.
Agglutinogen - An antigen that stimulates production of a specific antibody (agglutinin) when introduced into a host animal body. Outdated term for red-cell antigen.
Air sole - An outsole or midsole incorporating an air pocket or cushion.
Albumin - One of a group of heat-coagulable, water-soluble proteins occurring in egg-white, blood serum, milk, and many animal and vegetable tissues.
Alcohol - An organic compound having a hydroxyl (-OH) group attached. The lower molecular weight alcohols, methanol (CH3OH), ethanol (C2H5OH), and propanol (C3H7OH), are water soluble.
Alcohol dehydrogenase (ADH) - The main enzyme that catalyzes the conversion of ethanol to acetaldehyde.
Aldehyde dehydrogenase (ALDH) - The enzyme that converts acetaldehyde to acetate.
Algorithm - A set of well-defined rules for the solution of a problem in a finite number of steps.
Aliphatic - One of the main groups of hydrocarbons characterized by the straightor branched-chain arrangement of constituent atoms. Aliphatic hydrocarbons belong to one of three subgroups: (1) alkanes or paraffins, all of which are saturated and comparatively unreactive; (2) the alkenes or alkadiens that are unsaturated (containing double [C=C] bonds) and are more reactive; (3) alkynes, such as acetylene (that contain a triple [C≡C] bonds).
Aliquot - A measured amount of liquid taken from the main portion.
Alkali - A basic substance (pH greater than 7) that has the capacity to neutralize an acid and form a salt.
Alkaline phosphatase - A phosphatase active in alkaline media.
Alkaloid - One of a group of nitrogenous organic bases, especially one of vegetable origin, having a powerful toxic effect on animals and man, such as nicotine, cocaine, strychnine, or morphine.
Alkanes - An aliphatic hydrocarbon having the chemical formula C6H2n+2. Also known as paraffin.
Alkyd resin - A class of adhesive resins made from unsaturated acids and glycerol; used as a bonding agent in paint and lacquers.
Allele - One of a series of alternative form of a gene (or VNTR) at a specific locus in a genome. In DNA analysis the term allele is commonly extended to include DNA fragments of variable length and sequence that may have no known transcriptional product but are detected in a polymorphic system.
Allele frequency - A measure of the commonness of an allele in a population; the proportion of all alleles of that gene in the population that is of this specific type.
Allelic marker - Allele form of a gene used to identify chromosomal segments suspected of association with a certain phenotype. For example, allelic markers may be used with a family pedigree in which a phenotype is common to identify chromosomal segments that contain the gene responsible for the phenotype.
Allometry - The growth of part of the body in relation to the growth of the whole.The adjective form is allometric.
Allotypes - Genetically determined polymorphic variants. The term was first introduced to describe the different antigenic forms of rabbit gamma globulins. It was later extended to include polymorphic variants of plasma proteins in general (e.g., haptoglobins, Gc groups) but now includes red cell and white cell polymorphisms.
Alloy -A solid form of the liquid mixture of two or more metals, or of one or more met als with certain nonmetallic elements, as in brass, bronze, or carbon steel.
Alu - A family of repeat DNA sequences, cleaved by the restriction enzyme Alu I, dispersed throughout the genomes of many animal species. The family consists of about 50,000 copies, at 300 bp each, per human genome.
Amino acid - The building blocks of proteins coded by triplets of bases in DNA blueprint. Any one of a class of organic compounds containing the amino (NH2) group and the carboxyl (COOH) group.
Ammonia - A colorless gaseous alkaline compound that is very soluble in water, has a characteristic pungent odor, is lighter than air, and is formed as a result of the decomposition of most nitrogenous organic material, such as tissue from dead bodies.
Amorph - (1) A gene that apparently has no end product, e.g., a specific antigenic determinant. Sometimes referred to as a silent gene.
(2) A mutation that obliterates gene function; a null mutation.
Amosite - A monoclinic amphibole form of asbestos having long fibers and a high iron content; used in insulation.
Amplification - The production of additional copies of a chromosomal sequence, found as intrachromosomal or extrachromosomal DNA.
Amplification blank - A control that consists of only amplification reagents without the addition of sample DNA. This control is used to detect DNA contamination of the amplification reagents and material. Also known as a kit reagent blank.
Amplified fragment length polymorphism (AMP/FLP) - Polymerase chainreaction amplified restriction fragment lengths consisting of a variable number of tandem repeats.
Amplify - To increase the strength or amplitude of extracted DNA. material.
Amylase - An enzyme found in plant and animal tissue that promotes the conversion of starch and glycogen into maltose.
Amyloidosis - A metabolic disorder marked by extracellular deposition of amyloid (an abnormal protein) in the tissues; this usually leads to loss of function and organ enlargement.
Analyte or Target analyte - Substance to be identified or measured.
Analytical - The branch of chemistry dealing with techniques that yield any type of information.
Analytical balance - Instrument used to measure out or weight different types of dry chemicals. The measurement for weighing the substance is designated as grams.
Analytical gel - A gel that consists of all the digested DNA evidence and control DNA samples for a particular forensic case.
Analytical run (series) - A set of measurements carried out successively by one analyst using the same measuring system, at the same location, under the same conditions, and during the same short period of time.
Analytical sensitivity - The ability of a method or instrument to discriminate between samples having different concentrations or containing different amounts of the analyte. The slope of the analytical calibration function.
Analytical specificity - Ability of a measurement procedure to determine solely the measurable quantity (desired substance) it purports to measure and not others.
Analytical wavelength - Any wavelength at which an absorbance measurement is made for the purpose of the determination of a constituent of a sample.
Anaphylaxis - An allergic hypersensitivity reaction of the body to a foreign protein or drug.
Angle of impact - The internal angle at which blood strikes a target surface relative to the horizontal plane of that surface. Thus, a straight-on impact would have an impact angle of 90°.
Anidex - A manufactured fiber in which the fiber-forming substance is any longchain synthetic polymer composed of at least 50% by weight of one or more esters of a monohydric alcohol and acrylic acid.
Anisotropic - Having different properties in different directions, i.e., when a fibrous substance conducts heat more rapidly along its fibers than across them. Exhibiting double refraction, as a lens or mineral. An object that has properties that differ according to the direction of measurement when viewed in polarized light.
Anneal - The formation of double strands from two complementary single strands of DNA and RNA. In the second step of each PCR cycle, primers bind or anneal to the 3’ end of the target sequence.
Annealing - The pairing of complementary single strands of DNA to form a double helix.
Anode - In an electrolytic cell, the electrode at which oxidation occurs; the positive terminal of an electrolytic cell.
Anonymous loci - Specific sites on a chromosome where the gene functions have not been identified.
Anthophyllite - A natural magnesium-iron silicate; a variety of asbestos occurring as lamellae, radiations, fibers, or massive in metamorphic rocks. Also known as bidalotite.
Antiparallel - A term used to describe the opposite orientations of the two strands of a DNA double helix; the 5’ end of one strand aligns with the 3’ end of the other strand.
Antisera - Injecting human serum into various animals, such as the horse, goat, sheep, rabbit, duck, hen, or guinea pig, can produce antihuman sera.
Aqueous solution - A solution with water used as a solvent.
Aramid - A manufactured fiber in which the fiber-forming substance is any longchain synthetic polyamide in which at least 85% of the amide linkage is attached directly to two aromatic rings.
Arsenic - (1) A chemical element (As). (2) A medicinal and poisonous element; a brittle steel-gray hexagonal mineral, the native form of the element.
Artificial decomposition scent - Chemicals produced commercially for scent training that reproduce compounds that occur during decomposition (putrescine and cadaverine).
Atomic emission spectroscopy - Technique based on the emission of light by excited, vaporized, and atomized elements. Excitation can arise from any of a number of energy sources. The instruments are usually polychromatic devices. The method is most useful for quantitative analysis; qualitative use is also popular.
Atomic mass spectroscopy -nTechnique based on detection of vaporized and atomized elements and their ionized isotopes. The detection and display of the spectra are based on the mass-to-charge ratios of the ions. The method is specific for qualitative analysis and also valuable for quantitative analysis.
Autorad - An x-ray film of the hybridization between the radioactive probe and the complementary exposed strand of DNA.
Autoradiogram - (autoradiography) A technique for detecting radioactivity in a specimen by producing an image on a photographic film or plate. A DNA probe tagged with a radioactive isotope such as 32P (radioactive phosphorus) is exposed to a piece of x-ray film where the probe hybridizes to complementary is exposed to a piece of x-ray film where the probe hybridizes to complementary sequences on the blot in contact with the film.
Autosome - Nonsex chromosome. There are 22 autosomes in the human genome.
Azeotrope - A mixture of two or more compounds that have a constant boiling point. The composition of the vapor above the azeotropic mixture has the same relative concentration of the compounds as does the boiling liquid.Azeotropic mixtures cannot be separated by fractional distillation.
Axon - The part of a nerve cell that conducts nervous impulses away from the nerve cell body to the remainder of the cell (i.e., dendrites); large number of fibrils enveloped by a segmented myelin sheath.
Azlon - Any textile fiber derived from protein, such as casein.
Backspatter - Blood that is directed back toward its source of energy. Backspatter is often associated with gunshot wounds of entrance.
Band - A radioactive signal on an autorad usually caused by a fragment of human or bacterial DNA that combines with a radiolabeled DNA probe.
Band-shifting - The phenomenon where DNA fragments in one lane of an electrophoresis gel migrate across the gel more rapidly than identical fragments in a second lane.
Barr bodies - A condensed, inactivated X-chromosome inside the nuclear membrane in interphase somatic cells of women.
Barrier filter - A filter used in fluorescence microscopy that suppresses unnecessary excitation light that has not been absorbed by the fiber and selectively transmits only the fluorescence.
Base sequence - The order of bases in a DNA molecule, example ATCGGACT.
Baselining - Adjusting the baselines of detected dye colors to the same level for a better comparison of relative signal intensity.
Base pair (bp) - A chemical bonding partnership composed of adenine (A) double bonding with thymine (T) and cytosine (C) triple bonding with guanine (G) coming together to form a DNA double-helix molecule.
Bases - Chemical units (adenine, thymine, guanine, and cytosine) whose order in DNA molecules governs the genetic code.
Batch or Analytical batch - Group of one or more specimens or samples that are analyzed under conditions approaching repeatability. Usually it should contain calibrators and quality-control specimens or samples in addition to the samples to be analyzed.
Becké line - The bright halo near the boundary of a fiber that moves with respect to that boundary as the microscope is focused through the best focal point.
Becké line method A- method for determining the refractive index of a fiber relative to its mountant by noting the direction in which the Becké line moves when the focus is changed. The Becké line will always move toward the higher refractive index medium (fiber or mountant) when focus is raised and will move toward the lower refractive index medium when focus is lowered.This is a traditional means for matching a particle with an immersion liquid.
Beer’s law T- he absorbance of a homogeneous sample containing an absorbing substance is directly proportional to the concentration of the absorbing substance.
Benzene - A hexagonal organic molecule having a carbon atom at each point of the hexagon, and a hydrogen atom attached to each carbon atom. Molecules that contain a benzene ring, are known as aromatic.
Benzidine - A grayish-yellow, white or reddish gray crystalline powder. It is used in organic synthesis and the manufacture of dyes, especially of Congo red. Also used for the detection of bloodstains and as a stiffening agent in rubber compounding.
Binder - The actual film-former that binds the pigments particles to one
another and to the substrate.
Biohazard bag - A container for materials that have been exposed to blood or other biological fluids, and have the potential to be contaminated with various diseases such as hepatitis, AIDS, or other viruses. The bag is a heavy plastic red color with the biohazard symbol printed on the outside.
Biological fluids - Fluids that have human or animal origin, most commonly encountered at crime scenes (e.g., blood, mucus, perspiration, saliva, semen, vaginal fluid, and urine).
Biological sample bag (Biobag) - A collection of biological stains such as saliva,seminal stains, bloodstains, and vaginal secretions, acquired from physical evidence from submitting agencies, sealed in a plastic bag. The items contained in the biobag can be swabs (vaginal, oral, anal, dried secretions),fingernail scrapings, control bloodstains or small cuttings from the physical evidence.
Biomechanics [ The science that cncerns itself with the structure and mechanical movements of parts of the body, such as the foot.
Birefringence - The splitting of a light beam into two components, which travel at different velocities, by a material.
Blind external proficiency test - A test that is presented to a forensic laboratory through a second agency and appears to the analysts to involve routine evidence. A proficiency test sample for which the analyst is unaware of the test nature of the sample at the time of analysis.
Blood group An immunologically distinct, genetically determined class of human erythrocyte antigens, identified as A, B, AB, and O. A classification of red blood cell surface antigens, ABO is the best known of the blood group systems.
Blood type - A way of saying which blood group antigens are present on the person’s red cells.
Bloodborne pathogen - Infectious, disease-causing microorganism that may be found or transported in biological fluids.
Bovine albumin - Any one of a class of protein substances found in the blood of a bovine animal. Also known as bovine albumin serum (BSA).
bp - An abbreviation for base pair; distance along DNA is measured in bp.
Bradycardia - Slow heart rate, usually fewer than 60 beats per minute.
Brentamine fast salt blue B A - chemical used for the detection of the enzyme acid phosphatase, which is found in high concentrations in seminal fluid.This chemical reagent is a preliminary screening test for the presence acid phosphatase in seminal fluid or on seminal-stained evidence.
Brentamine reaction - A chemical used for the detection of acid phosphatase, this enzyme is found in high concentrations in seminal fluid. This chemical reagent is a preliminary screening test for the presence of prostatic acid phosphatase in seminal fluid or on seminal-
stained evidence. This reaction relies on the liberation of naphthol from sodium-naphthly phosphate by the enzyme, acid phosphatase, and the concomitant formation of a purple azo dye by the coupling of naphthol with buffered Brentamine Fast Blue B.
Broad sense heritability (H2) - The proportion of total phenotypic variance at the population level that is contributed by genetic variance.
Buccal cells C- ells derived from the inner cheek lining. These cells are present in the saliva or can be gently scraped from the inner cheek surface.
Buffy coat - The whitish layer of cells (white blood cells plus platelets) overlaying the red cell pellet after centrifugation of whole blood.
Calibrant - Substance used to calibrate, or to establish the analytical response of, a measurement system. _
Calibrate - To determine, by measurement or comparison with a standard, the correct value of each scale reading on a meter or other device, or the correct value for each setting of a control knob.
Calibration - (1) Set of operations that establishes, under specified conditions,the relationship between values indicated by a measuring instrument or measuring system, or values represented by a material measure, and the corresponding known values of a measurement. (2) Determining the response of some analytical method to known amounts of a pure analyte.
Calibration curve - Relationship between the signal response of the instrument and various concentrations of analyte in a suitable solvent or matrix.
Calibrator - Pure analyte in a suitable solvent or matrix, used to prepare the calibration curve.
Calorie - The amount of energy required to raise the temperature of 1 g of water by 1°C.
Candidate match - A possible match between two or more DNA profiles discovered by CODIS software. Qualified DNA analysts must verify candidate matches.
Capillary (Gas chromatography) - A narrow-bore glass tube. Gas chromatography employs glass tube capillary columns having an inside diameter of approximately 0.2 to 0.5 mL and a length of 3 to 300 m. The walls of a capillary column are coated with an adsorbent or adsorbent medium (a liquid phase in which the sample dissolves)
Carbon - The element upon which all organic molecules are based
Carbon dioxide - a molecule consisting of one atom of carbon and two atoms of oxygen, which is a major combustion product of the burning of organic materials. Carbon dioxide (CO2) is the result of complete combustion of carbon.
Carbon monoxide (CO) - A colorless, odorless, very toxic gas, formed by burning carbon or organic fuels. A gaseous molecule having the formula CO, which is the product of incomplete combustion of organic materials.Carbon monoxide has an affinity for hemoglobin that is approximately 200 times stronger than that of oxygen. It is highly poisonous.
Cast-mold - Three-dimensional representation of a footwear impression left at a crime scene. Cast-molds can be made from dental stone or plaster of paris,which are gypsum-plaster products. Cast-molds can also be used for teeth and tire impressions.
Cast-off pattern - Blood that has been projected onto a surface from other than an impact site. This pattern is produced when blood is thrown from a bloody object in motion.
Casual shoe - A shoe designed for easy, informal wear, normally having a leather upper and either a leather or a soft synthetic shoe.
Catalyst - A substance that increases the rate of chemical reaction without undergoing a permanent change in its structure.
Catecholamines - Substances of a specific chemical nature (pyrocatechols with an alkylamine side chain). Cathecholamines of biochemical interest are those produced by the nervous system (e.g., epinephrine [adrenaline] or dopamine) to increase heart rate and blood pressure, or medicines with the same general chemical structure and effect.
Cathode - The electrode at which reduction takes place in an electrochemical cell.
Cation - A positively charged atom, or group of atoms, or a radical that moves to the negative pole (cathode) during electrolysis.
Caustic - Having the ability to strongly irritate, burn, corrode, or destroy living tissue.
Centrifuge A- rotating device for separating liquids of different specific gravities or for separating suspended colloidal particles, such as clay particles in an aqueous suspension, according to particle-size fractions by centrifugal force.
Chelex - A chelating resin that has a high affinity for polyvalent metal ions. It is composed of stytrene divinylbenzene copolymers containing paired iminodiacetate ions, which act as chelating groups.
Chemical color tests - Chemical reactions producing colors when compounds or classes of compounds are brought into contact with various chemical reagents.
Chemical change - Rearrangement of the atoms, ions, or radicals of one or more substances, resulting in the formation of new substances, often having entirely different properties. Also known as a chemical reaction.
Chemical enhancement - The use of chemicals that react with specific types of evidence (e.g., blood, semen, lead, fingerprints) in order to aid in the detection or documentation of evidence that may be difficult to see.
Chemical etching - A form of texturing a mold utilizing an acid bath that erodes selective portion of the metal, leaving a resulting texture or pattern.
Chemical formula - The collection of atomic symbols and numbers that indicates the chemical composition of a pure substance.
Chemical ionization - A type of mass spectrometry in which a molecule reacts under relatively low energy with a reagent gas rather than fragmenting extensively.
Chemical-protective clothing - Clothing specifically designed to protect the skin and eyes from direct chemical contact. Descriptions of chemical-protective apparel include nonencapsulating and encapsulating (referred to as liquidsplash protective clothing and vapor-protective clothing, respectively).
Chemical threat - Compounds that may pose bodily harm if touched, ingested,inhaled, or ignited. These compounds may be encountered at a clandestine laboratory, or through a homemade bomb or tankard leakage (e.g., ether,alcohol, nitroglycerin, ammonium sulfate, red phosphorus, cleaning supplies,gasoline, or unlabeled chemicals)
Chemiluminescence - Nonradioactive method for DNA analysis using VNTR probes that are tagged with alkaline phosphatase, which reacts with a detection reagent to generate light. The light produces an image on an x-ray film.
Chemistry - A basic science concerned with (1) the structure and behavior of atoms (elements); (2) the composition and properties of compounds; (3) the reactions that occur between substances and the resultant energy exchange; and 4) the laws that unite these phenomena into a comprehensive system.
Chimera - An organism whose cells derive from two or more distinct zygote lineages, e.g., the vascular anastomoses that may occur between twins (a twin of genetic type O may have a bone marrow implantation from its twin of group A; throughout life, therefore, he has a major red cell population of group O and a minor population of red cells of group A).
Chi-square (χ2) - A statistical test to determine how closely an observed set of data values corresponds to the values expected, under a specific hypothesis.
Chitin - A nitrogenous polysaccharide formed primarily of units of N-acetyl glucosamine occurring in the cuticle of arthropods.
Chlordiazepoxide hydrochloride - Crystals, toxic in high concentration, that are one type of central nervous system depressant.
Chloroform - An early use of chloroform was that of an anesthetic in some types of surgeries. Chloroform undergoes considerable biotransformation in man, with the formation of carbon dioxide and hydrochloric acid.
Christmas tree stain - Two chemicals used together to stain sperm cells;Kernechtrot solution will stain the head of the sperm cell a two-tone
reddish pink color and the picroindigocarmine solution will stain the tail
of the sperm cell a bluish green color.
Chromatin - A darkly staining substance located in the nucleus of the cell that contains the genetic material composed of deoxyribonucleic acid (DNA) attached to a protein structure.
Chromatogram - The complete array of distinctively colored bands produced by chromatography. A series of peaks and valleys printed or written on a paper chart where each peak represents a component or mixture of two or more unresolved components in a mixture separated by gas or liquid chromatography.
Chromatography - A method for the separation and analysis of small quantities of substances by passing a solution through a column of finely divided powder that selectively adsorbs the constituents in one or more sharply defined, often colored, bands. This method for separation can be done using thin-layer silica plates.
Chromogen - Any organic coloring matter or substance capable of yielding a dye.
Chromosome - A nuclear structure in eukaryotes that carries a portion of the genome. The human has 46 chromosomes per nucleus, 22 homologous pairs of autosomes, and 2 sex chromosomes.
Chromosome theory of inheritance - The unifying theory stating that inheritance patterns may be generally explained by assuming that genes are located in specific sites on chromosomes.
Chronic exposure - Repeated encounters with a hazardous substance over a period of long duration.
Chronograph - An instrument for recording graphically the moment or duration of an event, measuring intervals of time.
Chrysotile - A fibrous form of serpentine that constitutes one type of asbestos.
Cicero - A typographic unit of measurement used predominantly in Europe. It consists of 12 Didot points, each measuring 0.01483 in. Thus, a Cicero is 0.1776 in. or 4.511 mm.
Clone - Describes a large number of cells or molecules identical with a single ancestral cell or molecule.
Coefficient of relationship (r) - The proportion of genes that any two individuals have in common. It is the proportion of the genomes inherited from a common ancestor, or the probability that two individuals have inherited a specific gene or DNA fragment from a common ancestor.
Coefficient of variation (CV) or Relative standard deviation - Measure used to compare the dispersion of variation in groups of measurements. It is the ratio of the standard deviation (SD) to the mean (X), multiplied by 100 to convert it to a percentage of the average. CV = SD X × 100.
Cold match - A cold match occurs when CODIS matches two DNA profiles with no prior indication that the profiles are related. One profile may be in the offender index and the other in the forensic index, or both profiles may be in the forensic index. Cold matches must be confirmed by qualified DNA analysts.
Collagen A fibrous insoluble protein found in the connective tissue, including skin, bone, ligaments, and cartilage; represents about 30% of the total body protein.
Comparison - The act of setting two or more items side by side to weigh their identifying qualities. It implies not only a visual but also a mental act in which the elements of one item are related to the counterparts of the other.
Comparison microscope - Essentially two microscopes connected to an optical bridge that allows the viewer to observe two objects simultaneously with the same degree of magnification. This instrument can have a monocular or binocular eyepiece.
Comparison samples - A generic term used to describe physical material/evidence discovered at crime scenes that may be compared with samples from persons, tools, and physical locations. Comparison samples may be from either an unknown/questioned or a known source.
Complete digestion - The action of a restriction enzyme in completely cutting the DNA at a specific site.
Compound - A chemical combination of two or more elements, or two or more different atoms arranged in the same proportions and in the same structure throughout the substance. A compound is different from a mixture in that the components of a mixture are not chemically bonded together.
Compression molded - A molding method, in which a molding compound is placed into an open mold cavity, after which the mold is closed as heat and pressure are applied, causing the molding compound to melt and conform to the size and shape characteristics of the mold cavity.
Concentration - The amount of a substance in a stated unit of a mixture or solution. Common methods of stating concentration are percent by weight,percent by volume, or weight per unit volume. Amount of a drug in a unit volume of biological fluid, expressed as weight/volume. Urine concentrations are usually expressed either as nanograms per milliliter (ng/ml),micrograms per milliliter (μg/ml), or milligram per liter (mg/l). Example:there are 28,000,000 micrograms in an ounce, and 1000 nanograms in a microgram.
Concentric fractures - Patterns of cracks in glass pierced by a missile like a bullet, which runs between the radial fractures and which originate on the side of the glass from which the impact came.
Conclusion - A scientific conclusion results from relating observed facts by logical,common sense reasoning in accordance with established rules or laws.
Confirmatory test - Second test by an alternative chemical method for unambiguous identification of a drug or metabolite. In serology, a chemical reaction that confirms the presence of a blood stain as human or nonhuman in origin.
Core - A fiber or fibers running lengthwise through the center of a cordage.
Corrosion The degradation of metals or alloys due to reaction with the environment.The corrosive action on the metals or alloys is accelerated by acids, bases, or heat.
Corrosive - Having the ability to destroy the texture or substance of a tissue.
Cortex - The middle layer of human hair containing the particles of pigment that gives the hair its individual color. The main structural component of hair consisting of elongated and fusiform (spindle-shaped) cells. The cortex may contain pigment grains, air spaces called corticalfusi, and structures called ovoid bodies. Also refers to the outer layer of an organ such as the brain or kidney.
Crepe rubber - A natural, unvulcanized rubber used for soles and heels. Most crepe rubber made today is synthetic crepe rubber.
Critical reagents - Reagents such as commercial supplies and kits that have an expiration date. A substance used because of its chemical or biological activity. These reagents are essential to certain chemical
Cuticle - (Hair analysis) The protective outer sheath of the hair, formed by a series of overlapping scales.
Cut-off concentration - Concentration of a drug in a specimen or sample used to determine whether the specimen or sample is considered positive or negative. In some circumstances it is recommended that the cut-off concentration should be set equal to the limit of detection.
Cutoff level - (threshold) Value serving as an administrative breakpoint (or cutoff point) for labeling a screening test result positive or negative.
Cyanide (CN) - A highly toxic chemical especially in the form of gas (hydrogen cyanide).
Cyanosis - Bluish discoloration of the skin and mucous membrane due to deficient oxygenation of the blood; usually evident when reduced hemoglobin exceeds 5%. It is present in many heart and respiratory conditions.
Cytochrome - P450 A detoxifying enzyme found in liver cells.
Cytosine (C) - One of the four nucleotide bases in DNA.
Dark-field microscopy - Descriptive of the appearance of the image of the specimen when this technique is used. Various details of the specimen appear as bright features on a dark field or background. Dark-field microscopy can be used to accentuate refraction images.
Daubert test - A standard for determining the reliability of scientific expert testimony in court currently adopted by many jurisdictions. Five factors are utilized to assess the scientific theory or technique testing of theory, use of standard and controls, peer review, error rate, and acceptability in the relevant scientific community.
Decant - The process of pouring off the supernatant during separation from a pellet after a mixture has been centrifuged or left to settle.
Declination - The difference between true north as shown on a topographic map and magnetic north as indicated by the magnetic needle on a compass.
Decontamination - (1) Removal of hazardous materials from exposed persons and equipment after a hazardous materials incident. (2) In the forensic laboratory environment, the cleaning of work benches, scissors, forceps, and other instruments that have come in contact with physical evidence, with 10% bleach and 70% ethanol.
Degradation - The process of decomposition. When applied to protective clothing, a molecular breakdown of material because of chemical contact; degradation is evidenced by visible signs such as charring, shrinking, or dissolving.
Degree of wear - The extent to which a particular portion of the shoe is worn.
Delustering - The treatment of synthetic yarns and fabrics by special pigments or other chemicals in order to reduce their natural luster.
Delustrant - A substance used to produce dull surfaces on textile fabric; the more common ones are barium sulfate, clays, chalk, titanium dioxide. They are applied in the finishing coat.
Denaturation - (1) Describes the conversion of DNA from the double-stranded to the single-stranded state; separation of the strands is most often accomplished by heating. (2) A change in the molecular structure of globular proteins that may be induced by bringing a protein solution to its boiling point, or by exposing it to acid or alkalies or to various detergents.
Denier - A unit of rayon or silk yarn size, based on a standard weight of 5 cg per 450 m of silk.
Density gradient tube - Equipment for measuring the distribution of particles of different density in a soil sample by determining the point at which they are suspended in a glass tube filled with successive layers of liquid of different densities.
Deoxyribonucleic acid (DNA) - The molecule of heredity, a nucleic acid of complex molecular structure forming a principal constituent of the genes; known to play an important role in the genetic action of the chromosomes.DNA is composed of deoxyribonucleic building blocks, each containing a base adenine (A), thymine (T), cytosine (C), or guanine (G); a deoxyribose sugar (S); and a phosphate group (P).
Desiccate - To dry out thoroughly; to remove all moisture.
Diatoms - Microscopic organisms found in lake and river water that reveal by their presence whether a victim found in these surroundings died by drowning, or were already dead upon entering the water.
Dichroism - The property of exhibiting different colors, especially two different colors, when viewed in polarized light along different axes.
Diethylamine - Water-soluble, colorless liquid with ammonia aroma, used in rubber chemicals and pharmaceuticals, and as a solvent and flotation agent.
Differential extraction - A step-wise extraction procedure designed to separate intact sperm heads from lysed sperm and other cell types. The separation generally results in an enrichment of sperm DNA in one cell fraction relative to the other cell fractions. The separate fractions can be analyzed individually.
Diffuser - A material used to soften the original light and to disperse it to a degree.
Dilution - The use of water to lower the concentration or amount of a contaminant.
Dinitrotoluene (DNT) - An explosive used as a coating on gunpowder to retard the burning rate and to act as a moisture proofing agent.
Diphenylamine - Chemical reagent used in solution with sulfuric acid and acetic acid in the dermal nitrate test. Diphenylamine is also used in smokeless powder as a stabilizer to inhibit decomposition.
Direct attach - A process wherein the lasted upper of a shoe is lowered into the mold cavity after which the mold closes tightly around the shoe upper, after which the midsole or outsole is molded directly onto the upper.
Direction of flight - The trajectory or flight directionality of a blood drop that can be established by its angle of impact and directionality angle.
Dispersion of birefringence - The variation of birefringence with wavelength of light. When dispersion of birefringence is significant in a particular fiber, anomalous interference colors not appearing in the regular color sequence of the Michel–Levy chart may result. Strong dispersion of birefringence may also interfere with the accurate determination of retardation in highly birefringent fibers.
Dispersion staining - A technique for refractive index determination that employs a microscope. Using an annular stop with the substage iris closed, a fiber mounted in a high dispersion medium will show a colored boundary of a wavelength where the fiber and the medium match in refractive index.Using a central stop, the fiber will show colors complementary to those seen with an annular stop.
Distal - Indicates farther away from the center of the body.
Distillation - A separation process in which a liquid is converted to a vapor and the vapor is then condensed back to a liquid. The usual purpose of distillation is separation of the compounds of a mixture. Steam distillation separates all water-insoluble liquids from solids and water-soluble compounds in a mixture.
Dizygotic - Twins produced from two separate zygotes. Also called fraternal twins. On average, one-half of their genomes are shared.
DNA genetic analyzer - An instrument that can separate small fragments of DNA either by using gel electrophoresis or by using capillary electrophoresis.
DNA profile - A DNA profile consists of a set of DNA identification characteristics, i.e., the particular chemical form at the various DNA locations (loci) that permit the DNA of one person to be distinguishable from that of another person.
Double helix - The structure of DNA first proposed by Watson and Crick, with two interlocking helices joined by hydrogen bonds between paired bases.
Drier - A material that promotes or accelerates the drying, curing, or hardening
of oxidizable coating vehicles. The principal driers are metal soaps
of a monocarboxylic acid.
Drip pattern Blood that drips into blood, resulting in round, satellite blood spatters, 0.1 to 1.0 mm in diameter, around the periphery of the central bloodstain.
Drying oils - Naturally occurring triglycerides that form films principally by air oxidation. The same oils may be used as feed stocks for varnishes, alkyd resins, epoxy ester resins, oil-modified urethane resins, and some plasticizers.
Dyes - Soluble substances that add color to textiles. Dyes are classified into groups that have similar chemical characteristics (e.g., aniline, acid, and azo). They are incorporated into the fiber by chemical reaction, absorption,or dispersion.
Efface - To rub out, to strike or scratch out, or to erase.
Ejaculate - The semen released by one ejaculation.
Electromagnetic radiation - The energy (in the form or magnetic and electric fields) given off by a vibrating charge (such as an electron). Every physical object in the universe gives off electromagnetic radiation of one type or another. The phenomenon of sight is due to our eyes being sensitive to a certain type of electromagnetic radiation.
Electron - A negatively charged subatomic particle that circles the nucleus of the atom in a cloud. Most chemical reactions involve the making and breaking of bonds held together by the sharing electrons.
Electron capture detector (ECD) - A type of gas chromatographic detector that is sensitive to halogenated hydrocarbons and other molecules capable of easily gaining an electron. Electron capture is not generally used for hydrocarbon detection.
Electron microscope - A microscope that forms its image by the electrons emitted from the specimen when scanned by a focused beam of electrons.
Electronic flash - Lighting unit utilizing the flash of light produced by discharging a current between two electrodes in a gas-filled tube.
Electropherogram - Is a chromatographic display with fluorescence intensity indicated as relative fluorescence units (RFU) on the y-axis. After the internal lane size standard has been defined and applied, the electropherogram can be displayed with the base pair size on the x-axis. Fourcolor image of a sequence, showing peaks that represent the bases.
Electrophoresis The process of separating charged molecules, for example, negatively charged DNA fragments, in a porous medium such as agarose, by the application of an electric field. DNA separates according to size with the small fragments moving most rapidly.
Electrophoretic mobility - A characteristic of living cells in suspension and biological commons (proteins) in solution to travel in an electric field to the positive or negative electrode because of the charge on these substances.
Electrostatic detection apparatus - A device primarily used to detect indented writing on documents that can also be used to detect footwear impressions on paper items.
Electrostatic lifting device - A device consisting of a high-voltage supply used with a special conductive lifting film to electrostatically transfer a dry origin footwear impression from a surface to the film.
Element - One of 106 presently known substances that comprise all matter at and above the atomic level. A substance made up of atoms with the same atomic number; common examples are hydrogen, gold, and iron. Also known as chemical element.
Elute - To remove (adsorbed material) from an adsorbent by means of a solvent.The solvent mixture that acts as the mobile phase in thin-layer
Elution - The process of removing adsorbed materials from the surface of an adsorbent such as activated charcoal. The solvent in this process is called the eluant.
Emission spectroscopy - The study of the composition of substances and identification of elements by observation of the wavelength of radiation emitted by the substance as it returns to a normal state after excitation by an external source.
Enamel - The term enamel does not intimate the chemical nature of the
coating, but implies a pigmented coating that dries to a hard gloss. Increasingly, the term has come to mean a cross-linked thermosetting resin.
Enzyme - A recycling protein molecule that catalyzes a specific chemical reaction.Any of a group of catalytic proteins that are produced by living cells and that mediate and promote the chemical processes of life without themselves being altered or destroyed.
Ethidium bromide - A molecule that binds to DNA and fluoresces under ultraviolet light; used to identify DNA.
Ethylbenzene - A component of gasoline, but also a major breakdown product of pyrolysis released when certain polymers are heated.
Eukaryote - A multicellular organism having true membrane-bound nuclei containing chromosomes that undergo mitosis.
Eutectic - The lowest melting point of an alloy or solution of two or more substances (usually metals) that is obtainable by varying the percentage of the components. Eutectic melting sometimes occurs when molten aluminum or molten zinc comes in contact with solid steel or copper.
Eutrophic - The state of nutrient enrichment as a result of the natural or artificial addition of nutrients to bodies of water, especially lakes, often resulting in high productivity and low transparency.
Eversion - Raising of the outer border of the foot.
Excitation fiber - A fiber used in fluorescence microscopy that transmits specific bands or wavelengths of energy capable of inducing visible fluorescence in various substrates.
Extender - A low-cost white inorganic pigment used with other white pigment to modify the gloss, texture, viscosity, and other properties, and to reduce the cost of the finished product.
Extraction A chemical procedure for removing one type of material from another. Extraction is generally carried out by immersing a solid in a
liquid, or by shaking two immiscible liquids together, resulting in the
transfer of a dissolved substance from one liquid to the other. Solvent
extraction is one of the primary methods of sample preparation in arson
debris analysis. In DNA analysis, it is the extraction of DNA material
from the nucleus of nucleated cells.
Fibers - A common class of microscopic evidence. They are classified as animal, vegetable, mineral, or natural, manufactured, or synthetic. Some types of ropes are composed of numerous of fibers woven together to form the rope.
Fixatives - A spray or powder applied cautiously to a footwear impression prior to casting, to prevent it from loss of detail when the casting materials are applied to it.
Flight path - The path of the blood drop as it moves through space from the impact site to the target.
Flow pattern - A change in the shape and direction of a wet bloodstain due to the influence of gravity or movement of an object.
Fluorescence - Property possessed by various substances that glow when exposed to light of a short wavelength. The phenomenon in which some substances absorb light and re-emit part of it as light of a longer wavelength. Fluorescence ceases when incident or exciting illumination ceases.
Fluorescence microscope - A variation of the compound laboratory light microscope that is arranged to admit ultraviolet, violet, and sometimes blue radiations to a specimen that then fluoresces.
Fluorosis - Accumulation of excessive fluoride in the body, characterized by increased bone density and mineral deposits in tendons, ligaments, and muscles.
Footwear - Any apparel that is worn on the foot, such as a shoe, boot, etc.
Formaldehyde - A readily polymerizable gas. Commercial grades are called formalin. Used as embalming fluid, preservative, hardening agent, reducing agent, and durable-press treatment of textile fabrics. Formaldehyde is a highly toxic substance if inhaled or if it comes in contact with the skin.
Formula - A combination of chemical symbols that expresses a molecule’s composition.The reaction formula shows the interrelationship between reactants and products.
Formula weight - The gram-molecular weight of a substance.
Forward spatter - Blood that travels in the same direction as the source of energy or force causing the spatter. Forward spatter is often associated with gunshot wound of exit.
Fourier transform (FT) - A mathematical operation that converts a function of one independent variable to one of a different independent variable. In FT–IR spectrometry, the Fourier transform converts a time function (the interferogram) to a frequency function (the infrared absorption spectrum).Spectral data are collected through the use of an interferometer that replaces the monochrometer found in the dispersed infrared spectrometer.
Fourier transform infrared (FT–IR) spectrometry - A form of infrared spectrometry,in which an interferogram is obtained; this interferogram is then subjected to a Fourier transform to obtain an amplitude wavelength (or wavelength) spectrum.
Foxing - A component of the shoe used to reinforce or cover the edge of the shoe where the outsole and the upper join together. Usually a strip of rubber (foxing strip) wrapped around the lower part of the shoe.
Fraction - One of the portions of a volatile liquid within certain boiling point ranges, such as petroleum naphtha fractions or gas–oil fractions.
Fragile X syndrome - A complex inherited syndrome of mental retardation usually seen in males and associated with a tendency for the X chromosome to break in culture at a trinucleotide repeat site.
Fragment - (DNA analysis) A piece of DNA cut by a restriction enzyme, also known as a band on an autorad.
Frequency - (DNA analysis) Specifically refers to the number of individuals or measurements in a subgroup of the total group under consideration. The term is often more loosely equated to proportion, that is, to define a fraction or percent. (Criminalistics) The number of times per unit time that the magnitude of an electromagnetic wave goes from maximum to minimum, then back to maximum amplitude.
Frye standard - A set of standards established by the Court of Appeals of the District of Columbia in 1923 for Frye vs. the United States. The standards in general define when a new scientific test should be admissible as evidence in the court system.
Frye test - A test emphasizing that the subject of an expert witness’s testimony must conform to a generally accepted explanatory theory. Named after the case in which the determination was made.
Gallops - Relating to cardiac rhythms, an abnormal third or fourth heart sound in a patient experiencing tachycardia. Gallops are indicative of a serious heart condition.
Galvanic skin response (GSR) - The electrical conductance of the skin, one of the physiological responses measured by the polygraph or lie detector to ascertain whether or not a subject is telling the truth.
Gamete - A reproductive cell (egg or sperm). A specialized haploid cell that fuses with a gamete from the opposite sex or mating type to form a diploid zygote.
Gas - A physical state of matter that has low density and viscosity, can expand and contract greatly in response to changes in temperature and pressure,and readily and uniformly distributes itself throughout any container.
Gas chromatograph - Chromatograms from GCs are used to identify unknown compounds, such as debris collected from arsons, on the basis of the retention time or relative retention time of a peak under certain operating conditions.
Gas chromatography (GC) - A separation technique involving passage of a gas,as the mobile phase, moving through a column containing a fixed absorbent material; it is used principally as a quantitative analytical technique for volatile compounds or simple gases. The separation of organic liquids, such as gases or drugs into discrete components or compounds that are seen as peaks on a chromatogram. Separation is done in a column that is enclosed in an oven held at a specific temperature or programmed to change the temperature at a reproducible rate. The column separates the compounds according to their affinity for the material inside the column (stationary phase). Columns can be packed or capillary. Packed columns employ a powdery substance that may be coated with a nonvolatile liquid phase. A capillary column is a glass or quartz tube coated with a nonvolatile liquid.
Gasoline - A mixture of more than 20 volatile hydrocarbons in the range of C4 to C12, suitable for use in a spark ignited internal combustion engine.Regular automotive gasoline has a flash point of -40°F.
GC/MS (gas chromatograph/mass spectrometer) - A quantitative and qualitative method for the separation and identification of organic materials in complex mixtures or solutions. This method has applications in the examinations of drugs, explosive residues, paints, plastics and inks and can be used to analyze material to determine if a substance contains gunpowder.
Gel electrophoresis - Using a gel medium to separate charged molecules.
Gel electrophoresis unit and power pack - The unit is used for running gel electrophoresis systems. The unit can hold a small polyacrylamide gel, while the power pack supplies the electrical current needed to separate molecules,such as proteins or nucleic acids traveling through the polyacrylamide gel.
Gene The fundamental physical and functional unit of heredity that carries information from one generation to the next; a segment of DNA composed of a transcribed region and a regulatory sequence that makes transcription possible.
Gene frequency (allele frequency) - A measure of the commonness of an allele in a population; the proportion of all alleles of that gene in the population that are of this specific type.
Generic class - A group of fibers having similar, but not identical, chemical composition. A generic name applies to all member of a group and is not protected by trademark registration. Generic names for manufactured fibers include, for example, rayon, nylon, and polyester.
Genetic markers - Can be divided into two groups based on differences in biochemistry, method of detection, and their history of discovery. The two groups are the polymorphic antigen system, which is found on red blood cells and other cell surfaces, and the polymorphic soluble protein markers.
Genus A group of closely related species of organisms. The genus is given as the first part of a scientific name.
Glare - Intense light reflected off highly reflective surfaces such as water, glass,and very light-toned objects.
Glass - An inorganic substance in a condition that is continuous with, and analogous to, the liquid state of that substance. An inorganic product of fusion that has cooled to a rigid condition without crystallizing. A manufactured fiber in which the fiber-forming substance is glass.
Glue - A crude, impure, amber-colored form of commercial gelatin of unknown detailed composition produced by the hydrolysis of animal collagen;gelatinizes in aqueous solutions and dries to form a strong, adhesive layer.
Hair - (1) An appendage of the skin that grows out of an organ known as the hair follicle. (2) A thread-like outgrowth of the epidermis of animals,especially a keratinized structure in mammalian skin.
Heel - A separate component attached to the rear portion of the outsole. In a onepiece outsole, it is the raised area in the rear portion of the outsole. In a flat shoe, it is the heel area.
Hemizygous - The situation in which a chromosomal element has no complement.This is normal for haploid organisms, and for some genetic elements such as mtDNA in diploid organisms.
Hue - The name by which one color is distinguished from another.
Hybridization - DNA molecules are composed of two complementary halves that serve as templates for each other. Hybridization occurs when these halves separate and a half of different origin connects with one of the separated halves to form a hybrid molecule.
Hydrocarbon - An organic compound containing only carbon and hydrogen.
Hydrochloric acid Pertaining to or designating a colorless, corrosive, fuming acid, HCL, exceedingly soluble in water.
Hydrogen - The simplest element. Atomic number of 1. Hydrogen gas has a specific gravity of 0.694 (air = 1), so it is much lighter than air. Hydrogen is highly flammable, forming water upon combustion. Explosive limit is 4 to 75%.
Hydrogen bond - A relatively weak bond between a hydrogen (H) atom,covalently bound to a nitrogen (N) or oxygen (O) atom, and another atom. These bonds bind complementary DNA strands together. The bonds can be easily broken by increasing the temperature; a temperature of about 95°C will separate the bonds between double-stranded DNA molecules.
Hydrolytic reaction - One in which a covalent bond is broken with the incorporation of a water molecule.
Hydrophilic - Groups interact with water, so that hydrophilic regions of protein or the faces of a lipid bilayer reside in an aqueous environment. Having a strong affinity for binding or absorbing water, which results in swelling and formation of reversible gels.
Hydrophobic - Groups repel water, so that they interact with one another to generate a nonaqueous environment. Antagonistic to water; incapable of dissolving in water.
Hypervariable - Some segments of DNA molecules are identical or almost identical in all individuals while others show variability. A hypervariable is a DNA segment that is highly variable and differs in most individuals.
Hypervariable region - Locus with many alleles, especially those whose variation is due to variable numbers of tandem repeats.
Hypotheses, alternative and null - The two possibilities established by the social scientist before running a statistical test. The null hypothesis means nothing unusual is going on, the independent variable has no significant effect on the dependent variable and the results could have occurred by chance. The alternative hypothesis rejects the null and prophesies that the independent variable will affect the dependent variable.
Hypothesis testing or Significance testing - Process of assessing the statistical significance of a finding. It involves comparing empirically observed sample findings with theoretically expected findings, expected if the null hypothesis is true. This comparison allows one to compute the probability that the observed outcomes could have been due to chance alone.
Immiscible - Describes substances of the same phase or state of matter (usually liquid) that cannot be uniformly mixed or blended.
Immunochemistry - That branch of chemistry concerned with the various defense mechanisms of the animal organism against infective agents, particularly the response between the body and foreign macromolecules (antigens), and the interaction between the products of the response (antibodies) and the agents that have elicited them. This involves study of the many proteins involved in these responses.
Immunodiffusion - It involves the use of agar plates with wells for both antibodies and antigens. The two reactants diffuse into the gel where immunoprecipitates will form at the point of equivalence for each
Immunoelectrophoresis - Consists of a combination of electrophoresis and immunodiffusion in a gel. It is based on the fact that in a gel medium, the movement of molecules in an electric field is similar to that in a liquid medium, with the advantage that free diffusion is lessened after electrophoresis.
Impact pattern Bloodstain pattern created when blood receives a blow or force resulting in the random dispersion of smaller drops of blood.
Impact site - The point on a bloody object or body that receives a blow. Often,impact site is used interchangeably with point of origin. Impact site may also refer to an area on the surface of a target that is struck by blood in motion.
Impact spatter - Bloodstain pattern created when blood receives a blow or force resulting in the random dispersion of smaller drops.
Impurity - The presence of one substance in another in such low concentration that it cannot be measured quantitatively by ordinary analytical methods.
Inclusion - A crime suspect’s DNA identity profile matching that of a crime evidence sample, or a putative father’s DNA identity profile matching offspring paternally derived alleles.
Infrared spectrometer - Device used to identify and measure the concentration of heteroatomic compounds in gases, in many nonaqueous liquids, and in some solids.
Infrared spectrophotometry (IR) - An analytical technique that utilizes an instrument that passes infrared radiation through a sample, or that bounces infrared radiation off the surface of a sample.A very sensitive heat detecting device measures the amount of infrared radiation absorbed as the wavelength of the radiation reaching the detector is changed. IR can give useful information about the type of compounds present in a sample, but it is not capable of precisely identifying a complex mixture. Infrared is very useful in identifying single solvent accelerants. Operates in the IR wavelength range. IR is employed by forensic scientists in the analysis of the following samples: drugs, plastics, fibers, paint, and similar substances.
Injection port - The area on a gas chromatograph or a high-performance liquid chromatography where the sample is introduced into the instrument and onto the column.
Inorganic chemistry - The study of chemical reactions and properties of all the elements and their compounds, with the exception of hydrocarbons, and usually including carbides, oxides of carbon, metallic carbonates, carbon–sulfur compounds, and carbon–nitrogen compounds.
Inorganic fiber - A class of fibers of natural mineral origin (e.g., chrysotile asbestos) and man-made mineral origin (e.g., fiberglass).
Inorganic pigment - A natural or synthetic metal oxide, sulfide, or other salt used as a coloring agent for paints, plastics, and inks.
Interfering substance - Substance other than the analyte that gives a similar analytical response or alters the analytical result.
Internal reflection spectroscopy (IRS) - The technique of recording optical spectra by placing a sample material in contact with a transparent medium of greater refractive index and measuring the reflectance (single or multiple) from the interface, generally at angles of incidence greater than the critical angle.
Internal standard - Addition of a fixed amount of a known substance that is not already present as a constituent of the specimen or sample in order to identify or quantify other components. The physico-chemical characteristics of the internal standard should be as close as possible to those of the analyte.
Interpretation - Explanation of what analytical results mean based on chemical, pharmacological, toxicological, and statistical principles.
Intumescent char - In plastics, the swelling and charring that results in a higher ignition point. Used in the preparation of flame retardant materials.
In vitro - Means “in glass” and refers to a biological process carried out in the laboratory separate from an organism.
In vivo - Refers to a biological process within a living organism.
Ion - An atom, molecule or radical that has lost or gained one or more electrons, thus acquiring an electric charge. Positively charged ions are cations;negatively charged ions are anions.
Isothermal - A type of gas chromatographic analysis wherein the column is maintained at a uniform temperature throughout the analysis.
Jig - A mechanical device that holds the correct position relationship between a piece of work and a tool or two pieces of work._
Karyotype - An individual’s set of chromosomes. Chromosomes arranged in order of length and according to position of centromere; also the abbreviated formula for the chromosome constitution, such as 47, XX + 21 for human trisomy-21.
Kb (kilobase) - An abbreviation for 1000 base pairs of DNA.
Kelvin - Unit of temperature (K) measurement used to measure the color temperature of light.
Kernechtrot solution - A reddish stain that is used in conjunction with picroindigocarmine solution in the identification of human sperm. The solution will turn the head of the sperm a reddish-pink color.
Ketone - A type of organic compound having a carbonyl functional group (C=O) attached to two alkyl groups. Acetone is the simplest example of a ketone.
Kinetics - A dynamic process involving motion.
Knit fabric - A structure produced by interloping one or more ends of yarn or comparable material.
Known sample technique - A quality assurance procedure in which a previously identified substance is submitted to a laboratory for examination to determine the reliability of the laboratory’s procedures.
Known standard A specimen of an identified source acquired for the purpose of comparison with an evidence sample; synonymous with exemplar.
Knurls or knurling - Regularly spaced ridges or rectangles used on a metal surface to assist in the prevention of slippage, usually on a knob.
Laboratory satellite A member of a laboratory system that is managed by, but is physically separated from, a parent laboratory.
Laboratory system - An organization containing at least two physically separate laboratory facilities that are independently managed under the control of a single laboratory director.
Lane of gel - The path in the gel within which DNA fragments migrate.
Langer’s lines - Structural orientation of the fibrous tissue of the skin that forms the natural cleavage line present in all body areas but visible only in certain areas such as the creases of the palm.
Laser - A device that uses the maser principle of amplification of electromagnetic waves by stimulated emission of radiation, and operates in the optical or infrared regions.
Latex - A suspension of a pigment in a water-based emulsion of any of
several resins, for example, acrylic polymers, vinyl polymers, or styrene–butadiene polymers.
Lattes crust method - This method relies upon the presence of the agglutinins in a bloodstain, and it is an application only to the ABO system. Adding indicator cells to the blood crust or bloodstain and testing for agglutination is a convenient way to detect the presence of agglutinin.
LCMS (liquid chromatography–mass spectrometry) - A technique that replaces a gas chromatograph with a liquid chromatograph. The technique is generally applicable to solutes that are soluble in organic solvents and not ionized.
Lead - Element with the chemical symbol Pb and atomic number 82. Used in the fabrication of bullet and shot for its formability and lubrication properties.
Lead glass - Glass into which lead oxide is incorporated to give high refractive index, optical dispersion, and surface brilliance; used in optical glass.
Leucomalachite green (leuco) test - A catalytic test that is used for the detection of blood and blood stains. The test depends upon an oxidation reaction in which an oxidant, such as hydrogen peroxide, oxidizes a colorless material such as phenolphthalein or malachite green to a colored one. The test is named after the compound oxidized that is the leuco base of malachite green. Malachite green structurally resembles phenolphthalein and the leuco prefix merely refers to the colorless or reduced form of the compound. The term leuco comes from the literature of biological stains and dyes. A positive reaction will produce a bluishgreen color.
Level of significance - Probability that a result would be produced by chance alone, i.e., the probability of incorrectly rejecting the null hypothesis. It is, therefore, the probability of making a type I error.
Light microscope - A microscope that employs light in the visible or near-visible portion of the electromagnetic spectrum.
LIMS (Laboratory Information Management System) - Software package for collating, calculating, controlling, and disseminating analytical data.It can perform a variety of functions, from specimen or sample registration and tracking to processing captured data, quality control, and financial control and report generation. This system uses a bar code label for identification and tracking of various specimen or samples.
Linear regression - Method of describing the relationship between two or more variables by calculating a best-fitting straight line or graph.
Linkage - A measure of association between loci. Loci on different chromosomes are nonlinked. Those close together on the same chromosome are closely linked and are usually inherited together.
Linkage disequilibrium - The phenomenon of a specific allele of one locus being associated or linked to a specific allele or marker of another locus, on the same chromosome, with a greater frequency than expected by chance.
Linkage equilibrium (LE) - When two or more genetic loci appear to segregate randomly in a given population. The genotypes appear randomly with respect to each other.
Locard’s exchange principle - According to Edmond Locard, when two objects contact each other, materials are transferred from one object to another;the basis for proving contact by the analysis of microscopic evidence.
Locus (plural, loci) - The site on a chromosome where a gene or a defined sequence is located. The position on a chromosome occupied by a gene.
Low-velocity impact spatter - Bloodstains produced on a surface when the blood source has been subjected to a low-velocity force approximately 5 ft/sec or less.
Lumigraph - A sheet of x-ray film with the results of quantified DNA that is measured in ng/uL.
Luminesce - To absorb illumination and re-emit it at a wavelength different from the incident light; akin to fluorescence, luminescence is useful to criminal investigation in that latent fingerprints become visible because organic solids in perspiration can be detected by lasers due to their luminescence.
Luminol - A substance that can be sprayed onto furnishings at a crime scene to reveal traces of blood as spots of bright light.
Luminol test - A method of choice for the detection of occult (usually not noticeable to the naked eye) blood at a crime scene that was cleaned up or escaped detection for extended periods of time.
Luster - The gloss or shine possessed by a fiber, resulting from its reflection of light. The luster of manufactured fibers is often modified by use of a delustering pigment.
Lymphocyte - A general class of white blood cells that are important components of the immune system of vertebrate animals.
Lyocel - A manufactured fiber composed of precipitated cellulose and produced by a solvent extrusion process where no chemical intermediates are formed.
Lysis - The process by which cells are broken apart and/or the process of disintegration or destruction of cells.
Lysis agent - A chemical used to open cell membranes and the cell’s nucleus,which will allow DNA from the cell to go into the extraction solution.
Magenta - A reddish-blue (minus green) color.
Manufactured fiber - A class name of various families of fibers produced from fiber-forming substances that may be synthesized polymers, modified or transformed natural polymers and glass.
Mass spectrometer - A mass spectroscope in which a slit moves across the paths of particles with various masses, and an electrical detector behind it records the intensity distribution of masses.
Mass spectrometry - An analytical technique for identification of chemical structures, determination of mixtures, and quantitative elemental analysis,based on application of the mass spectrometer. A method of chemical analysis which vaporizes, then ionizes the substance to be analyzed, and then accelerates the ions through a magnetic field to separate the ions by molecular weight. Mass spectrometry can result in the exact identification of unknown compounds, and is a very powerful analytical technique,especially when combined with chromatography. The instrument used for this analysis is referred to as a gas chromatograph/mass spectrometer detector (GC/MSD).
Match - When genetic profiles show the same types at all loci tested and no unexplainable differences exist.
Matrix - Consists of at least five fluorescently labeled DNA
fragments for each dye that are run and analyzed in separate lanes.
Mechanical pipettes - Hand-held pipettes that can deliver a specific volume of liquids; one can use the dial on the pipette to select the desired volume.There are different types of pipettes depending on what volume of liquid is needed.
Medium-velocity impact spatter - Bloodstains produced on a surface when the blood source has been subjected to a medium-velocity force between approximately 5 and 25 ft/sec. A beating typically causes this type of spatter. The preponderance of individual spots of blood produced in this manner are usually 1 to 3 mm in diameter, but larger and smaller spots can occur.
Medulla - Marrow of bones; central part of an organ or tissue; pith or central portion of stem. The central portion of a hair composed of a series of discrete cells or an amorphous spongy mass. A cellular column that runs through the center of the cortex. It may be air-filled, and if so, will appear opaque or black using transmitted light or white using reflected light. In animal hair, several types have been defined as uni- or multi-serial ladder,cellular or vacuolated, and lattice.
Mega - A prefix meaning 105 units (symbol M). One megagram equals 1,000,000 grams.
Meiosis - The process whereby a sex cell nucleus, after chromosomal replication,divides twice to form four nuclei each with one half the original chromosome number.
Melanin - Black or dark-brown pigment most frequently seen in skin and hair.
Melting - The denaturation point in referring to DNA.
Melting temperature (Tm) - The midpoint of the temperature range over which DNA is denatured.
Membranes - Consist of an asymmetrical lipid bilayer that has lateral fluidity and contains proteins. The coating of a biological cell, in and through which the osmotic mechanism of nutrient supply operates.
Mendel’s law - (Segregation) During meiosis, only one member of each homologous chromosome pair is transferred to a specific gamete. (Independent assortment) During meiosis, the members of the different homologous chromosome pairs assort independently when transferred to a specific gamete; for an example, AA ′ and BB
′ homologous chromosome pairs could give rise to AB, AB′, A
′B or A′B′ possible gametes.
Mercerized cotton - Cotton that has been strengthened by passing through a 25 to 30% solution of sodium hydroxide under tension, and then washed with water while under tension. This causes the fibers to shrink, increasing their strength and attraction for colors, as well as imparting luster.
Mercuric iodide - Red, tetragonal crystals, turning yellow when heated to 150°C.Used in medicine and analytical reagents (Nessler’s reagent and Mayer’s reagent).
Meta-ethyltoluene (m-ethyltoluene) - A chemical compound that can be found in gasoline.
Metallic paint - Paint used for covering metal surfaces; the pigment is commonly iron oxide.
Metallic pigment - Thin, opaque aluminum or copper alloy flakes that are incorporated into plastic masses to produce metal-like effects.
Metameric - Two or more materials that appear the same color under one type of illumination and different under another. Spectral analyses can differentiate metameric pairs.
Meter - The basic unit of length of the metric system, abbreviated with the letter m.
Methanol - Methyl alcohol or wood alcohol. The simplest alcohol that is water soluble and has a flash point of 54°F and an explosive limit of 6 to 36.5%.
Method traceability - Property of a method whose measurements give results that can be related with a given uncertainty to a particular reference, usually a national or international standard, through an unbroken chain of comparisons.
Methyl silicone - A nonvolatile oily liquid used in gas chromatography to separate nonpolar compounds. Methyl silicone columns typically separate compounds according to their boiling point.
Michel–Levy chart - A chart relating thickness, birefringence, and retardation so that any one of these variables can be determined for an anisotropic fiber when the other two are known.
Micro - A prefix representing 106, or one-millionth.
Microanalysis - Application of a microscope and microscopy techniques to the observation, collection, and analysis of microevidence.
Microcrystal tests - A reaction between the compound of interest and chemical reagent that results in the formation of unique crystals that can be observed with the microscope.
Microfuge - A high-speed (usually 10,000 rpm and faster) centrifuge for the centrifugation of small (usually <2 ml) specimens.
Micrometer - An instrument for measuring very small distances or dimensions.A caliper or gauge arranged to allow minute measurements. Abbreviated as (m). Also known as micron (μm).
Micrometry - A device utilizing a scale calibrated with stage micrometer for measurement of the physical dimensions of material viewed with a microscope.
Microsatellite - Short tandem repeat or simple sequence length polymorphism composed of di-, tri-, tetra-, or pentanucleotide repeats of nucleotides.
Microscope - An optical instrument consisting of a combination of lenses that allows the operator to view a magnified image of a small object.
Microscopist - An individual who uses a microscope to examine minute particles,hairs, fibers, and objects unable to be seen by the naked eye.
Microsomal enzymes - Detoxifying enzyme associated with certain membranes (smooth endoplasmic reticulum) within cells.
Microspectrophotometry - Instruments that generate transmission, reflection, or absorption spectra from various translucent and opaque samples. The principal types are visible and infrared.
Microtome - An instrument for making very thin sections for microscopic observations.
Midsole - A component found on some shoes that is often different in color, density,or materials, and is located between the outsole and the shoe upper.
Mineral spirits - A medium petroleum distillate ranging from C8 to C12. The flash point of mineral spirits is generally around 100°F. Mineral spirits,sometimes known as mineral turps, is commonly used as a solvent in insecticides and certain other household products. Many charcoal lighter fluids are composed almost entirely of mineral spirits.
Minisatellites - Regions of tandem repeats sequence DNA scattered throughout animal (and probably plant) genomes. Simple sequence tandem repeat polymorphism in which the core repeat unit is usually 10 to 50 nucleotides long; variable number of tandem repeats.
Misting - Blood which has been reduced to a fine spray as the result of the energy or force applied to it.
Mitochondria - A DNA-containing cytoplasmic organelles of eukaryotes. Mitochondria are referred to as the powerhouse of the cell because of the site for ATP production. The DNA in the mitochondria has a maternal inheritance.
Mitosis - The cell division that produces daughter cells with the same number of chromosomes as the original cells. All cell division, with the exception of that which produces mature sex cells, is mitotic.
Mixture - A heterogeneous blend of elements or compound that may or may not be uniformly dispersed. All solutions are uniformly dispersed mixtures.
Mobile phase - The movement of the liquid phase used for development of drugs spotted on thin-layer chromatography silicon plates. In gas chromatography,the mobile phase is the inert carrier gas that moves the volatile analytes through the length of the column.
Modacrylic fiber - Generic name for a manufactured fiber in which the fiberforming substance is any long-chain synthetic polymer composed of less than 85% but at least 35% by weight of acrylonitrile units. Characterized by moderate tenacity, low water absorption, and resistance to combustion,it also is self-extinguishing.
Molal - A concentration in which the amount of the solute is stated in moles and the amount of the solvent in kilograms.
Molar - A concentration in which one molecular weight in grams (one mole) of a substance is dissolved in one liter of solution. Molarity is indicated by an italic capital M. Molar quantities are proportional to the molecular weight of the substance.
Monomer - The simplest unit of a polymer. Ethylene is the smallest of polyethylene.Styrene is the smallest unit of polystyrene.
Monozygotic - Twins produced from a single zygote that later splits and develops identical genomes.
Morphology - The science of form and structure of plants and animals, as distinct from consideration of functions.
Mortality - The death rate; ratio of number of deaths to a given population.
Mosaic - An individual composed of two genetically different cell lines originally derived from the same zygote.
mtDNA - Maternally inherited mitochondrial DNA; present in 1000 to 10,000 copies per mammalian cells.
Multi-locus probe - A DNA probe that detects genetic variations at multiple sites; an autoradiogram of a multi-locus probe yields a complex, stripelike pattern of 30 or more bands per individual. This pattern was originally called a “DNA fingerprint” by its originator Alec Jeffreys.
Mummification - The drying, shrinking, and hardening of dead flesh due to extreme dehydration.
Mutation - Any change in the sequence of genomic DNA. May result from one or many base pair changes. A change in a gene’s DNA sequence resulting in the formation of another allele.
Myiasis - The invasion of any living vertebrate animal, including people, by fly larvae, especially maggots.
Nanogram (ng) - One billionth (10-9) of a gram.
Nanometer - A term for millimicron, as used in UV and infrared measurements.A unit of length equal to one-billionth of a meter or 10-9 meters.
Naphtha - An ambiguous (and obsolete) term that may mean high-flash naphtha (mineral spirits), or low-flash naphtha (petroleum ether, low boiling ligroin) or something altogether different. Flash points and explosive limits may vary.
Natural fibers - A class of fibers of vegetable (e.g., cotton, flax, ramie), animal origin (e.g., silk, wool, and specially fur), or mineral origin (e.g., asbestos).
Natural gas - A mixture of low-molecular-weight hydrocarbons obtained in petroleum-producing regions throughout the world. Natural gas consists of approximately 85% methane, 10% ethane with the balance propane,butane, and nitrogen. Because it is nearly odorless, an odorizing agent is added to most natural gas prior to final sale.
Neurotoxin - A poisonous substance in snake venom that acts as a nervous system depressant. Toxic substance that affects the brain and its neural pathways,causing psychological and physical problems.
Neutralize - To make a solution neutral pH of 7 (either acidic or basic) by adding a base to an acidic solution, or by adding an acid to a basic
Neutron activation analysis - Technique for identifying substances by bombarding a sample with neutrons in a nuclear reactor and measuring the energies and intensities of the resulting gamma rays.
Nicad - Nickel cadmium (NiCd) rechargeable battery.
Ninhydrin (triketohydrindene hydrate) - A strong oxidizing agent that causes the oxidative deamination of the α-amino function. The products of the reaction, which are the resulting aldehyde, ammonia, carbon dioxide,hydrindantin, and reduced derivatives of ninhydrin. The ammonia produced in this way can react with the hydrindantin and another molecule of ninhydrin to yield a purple product.
Nitrate - To treat or combine with nitric acid or a compound, to change into a nitro derivative.
Nitrite - A salt of nitrous acid.
Nitrocellulose - Pulpy, cotton-like, amorphous solid (dry), colorless liquid to semisolid (solution). Used for fast-drying automobile lacquers, high explosives, and leather finishing.
Nitrogen - A gaseous element that makes up approximately 80% of the Earth’s atmosphere. Nitrogen is relatively inert and does not support either combustion or life. Nitrogen is usually found in the molecular N2 form.
Nonsperm cell fraction - In a differential extraction, the portion of a sample containing DNA isolated from nonsperm cells.
Nonsperm cells - Any cell not derived from a male gamete.
Normality (N) - Measure of the number of gram-equivalent weights of a compound per liter of solution.
Nuclear DNA - The DNA contained within the nucleus of a cell. It constitutes the vast majority of the cell genome.
Nuclear fast red - Biological stain used to differentially stain spermatozoa to aid in their identification. It stains their nuclear material a dark red.
Nuclear magnetic resonance (NMR) - A phenomenon exhibited by a large number of atomic nuclei, in which in a static magnetic field absorbs energy from a radio frequency field at certain characteristic frequencies.
Nuclease - An enzyme that can degrade a DNA molecule by breaking its phosphodiester bonds.
Nucleic acid - A general class of molecules that are polymers of nucleotides.DNA is a nucleic acid.
Nucleotide - A molecule composed of a nitrogen base, a sugar, and a phosphate group; the basic building block of nucleic acid. A building block of DNA or RNA.
Nucleotide pair - A pair of nucleotides (one in each strand of DNA) that are joined by hydrogen bonds.
Nucleus - A complex, spheroidal body surrounded by a thin membrane and embedded in the protoplasm of most plant and animal cells. It contains the chromatin that is essential in the processes of heredity, and is the directive center of all the vital activities of the cell, as assimilation,
metabolism, growth, and reproduction.
Nylon - A manufactured fiber in which the fiber-forming substance in any longchain synthetic polyamide in which less than 85% of the amide linkage is attached directly to two aromatic rings.
Nylon membrane - The nylon membranes are used in the Southern blotting method. The DNA to be analyzed is exposed to restriction enzymes and after being separated by agarose gel electrophoresis, the DNA fragments in the gel are denatured with an alkaline solution and transferred onto a nitrocellulase filter or nylon membrane by blotting, thus preserving the distribution of the DNA fragments in the gel.
Octane - (1) An alkane having the formula C8H18 and with a flash point of 56°F and explosive limits of 1 to 3.2%. (2) A measure of the resistance of a sample of gasoline to premature ignition (knocking), 100-octane fuel has the knocking resistance of 100% iso-octane (2,2,4-trimethyl pentane).Zero-octane fuel has the knocking resistance of n-heptane; 89-octane fuel has the knocking resistance of a mixture of 89% iso-octane and 11% nheptane.
Odorant - A substance possessing a perceptible odor.
Olfaction - The act of detecting scent, generally by respiration, transmitting impulses from the mucous membranes in the upper part of the nose via the olfactory nerve to the forebrain, where the information is translated into perceived odor.
Oligonucleotide - A polymer composed of a few, usually less than 100 nucleotides.Oligonucleotides are usually synthesized by automated machinery and used as primers in PCR and as probes.
OneStep ABAcard Hema Trace membrane test - This membrane test device was developed originally for the detection of occult blood in human feces,often associated with gastrointestinal pathologies. In forensic serology this membrane test provides a sensitive, reproducible, and reliable test for determining whether the blood stains found on criminal evidence are of human origin. The species specificity of the reaction is based on the recognition by antibodies of antigens displayed on human hemoglobin.A positive result produces a pink colored line at the test area; absence of this color line suggests a negative result.
Optical analysis - Study of properties of a substance or medium, such as its chemical composition or the size of particles suspended in it, through observation of effects on transmitted light, such as scattering, absorption,refraction, and polarization.
Optical microscope - An instrument used to obtain an enlarged image of a small object, utilizing visible light; in general, it consists of a light source, a condenser, an objective lens, and an ocular or eyepiece that can be replaced by a recording device. Also known as a light microscope.
Organic chemistry - The study of the carbon atom and the compounds it forms,mainly with the 20 lightest elements, such as hydrogen, oxygen, and nitrogen. Some 3,000,000 organic compounds have been identified and named.
Organic compounds - Class of chemical compounds with carbon bases; all hydrocarbons are organic compounds.
Osmolality - The osmotic concentration of a solution determined by the ionic concentration of dissolved substances per unit of solvent.
Outsole - The outermost sole of a shoe. The portion of the shoe that contacts the ground and is exposed to wear.
Oxidation - Originally, oxidation meant a chemical reaction in which oxygen combines with another substance. Usage of the word has been broadened to include any reaction in which electrons are transferred. The substance that gains electrons is the oxidizing agent.
Oxygen - A gaseous element that makes up approximately 20% of the Earth’s atmosphere. It is usually found in the molecular O2 form. Oxygen is the most abundant element on earth.
Paint - A suspension pigment in an oil vehicle. It applies to virtually any
surface coating designed for protection of a surface or for decoration, or both. Sometimes the word paint may be a general term and the term surface coating is more specific.
Palindrome - A DNA site where the base order in one strand is the reverse of that in the complementary strand.
Paraffin - A translucent, waxy, solid mixture of hydrocarbons, indifferent to most chemical reagents; it is a constituent of peat, soft coal, and shale but is derived principally from the distillation of petroleum. Can come in rolls that are 2 or 4 in. wide and used to cover the top of glass test tubes or small plastic tubes.
Pathogen - An organism that causes disease in another organism.
Pentane - An alkane having the formula C5H12, with a flash point of -40°F, and with an explosive limit of 1.4 to 8%. Pentane is frequently used to extract flammable or combustible liquid residues from fire debris samples.
Permeation - The passage of chemicals, on a molecular level, through intact material, such as protective clothing.
Petroleum distillates - By-products of the refining of crude oil. Low-boiling or light petroleum distillates (LPD) are highly volatile mixtures of hydrocarbons.These mixtures are sometimes called ligroin, petroleum ether, or naphtha. LPDs are used as cigarette lighter fluids, copier fluid, and solvents.Medium-boiling petroleum distillates (MPDs) are sometimes
known as mineral spirits, and are used as charcoal starters, paint thinners,and solvent for insecticides. High-boiling or heavy petroleum distillates (HPDs) are combustible liquids such as kerosene and diesel fuel.
pH - The pH value of an aqueous solution is a number describing its acidity or alkalinity. A number used to represent the acidity or alkalinity of an aqueous solution.A solution with a pH of 7 is considered to be neutral;those solutions with pH below 7 are classified as acids. Bases have a pH above 7; the higher the pH, the solutions become more basic or alkaline.
pH electrode - Membrane-type glass electrode used as the hydrogen-ion sensor for most pH meters; the pH response electrode surface is a thin membrane made of a special glass (P.4; pH electrode on left).
pH meter - An instrument used to measure the degree of the acidity or the alkalinity of a solution: pH 7 (neutral), pH less than 7 (acidic), pH greater than 7 (alkaline)
Phadebas reagent - Commercial chemical consisting of a dye cross-linked to an insoluble starch. Upon digestion of the starch by amylase, the dye is released into solution. The intensity of color relates to the level of amylase present.This reagent is used for the detection of saliva stains on forensic evidence.
Pharmacokinetics - The study of the time course of the processes (absorption,distribution, metabolism, and excretion) a drug undergoes in the body.
Phenol (carbolic acid) - A poisonous and caustic organic compound, used in the isolation of DNA from cellular proteins.
Phenolphthalein - Pale yellow powder; forms an almost colorless solution in neutral or acid solution in presence of alkali, but colorless in the presence of a large amount of alkali. Used in dyes, acid-base indicator, and in medicine as a laxative.
Phenotype - The physical makeup of an individual as defined by genetic and nongenetic factors. Appearance of an inherited characteristic; the same appearance may be produced by different sets of alleles, and the same allele set may produce different appearances as a result of environmental and the interaction effects on gene expression.
Phosphatase - An enzyme that removes phosphate groups from different substrates.
Photoionization detector (PID) - A type of detector used in chromatography that employs ultraviolet radiation rather than a flame to ionize compounds as the particles pass through a detector. Photoionization detectors are particularly sensitive to aromatic compounds.
Picroindigocarmine solution - A greenish stain that is used in conjunction with Kernechtrot solution, for the identification of human sperm. This solution will stain the tail of the sperm cell a greenish–blue color.
Pigment - A finely powdered solid that is essentially insoluble in the medium in which is dispersed. Pigments may be inorganic, such as titanium dioxide,or organic, such as phthalocyanine. White pigments are primarily intended to hide the underlying surface. A pigment is distinguished from a dye in that a dye is soluble in the vehicle while a pigment is not.
Pipette A small glass or plastic tube, sometimes graduated, used for the removal of small portions of fluid and can be also used for measuring the volume of liquids.
Plaster - A very general term, including all gypsum casting materials. Also used to define the softer gypsum materials having a lower compressive strength.
Plaster of Paris - A gypsum material produced by heating crushed gypsum in an open oven at high temperatures. Can be used as dental and tool mark impressions.
Plasticizer - A material incorporated into a polymer to increase its flexibility or workability.
Point mutation - An alteration of one complementary nucleotide pair in chromosomal DNA that consists of addition, deletion, or substitution of paired nucleotides.
Point of convergence - A point to which a bloodstain pattern can be projected.This point is determined by tracing the long axis of well-defined bloodstains with the pattern back to a common point or source.
Point or area of origin - The three-dimensional point or area from which the blood that produced a bloodstain originated. This is determined by projecting angles of impact of well-defined bloodstains back to an axis constructed through the point or area of convergence.
Polarized light microscope (PLM) - A refined biological microscope stand to which several special purpose features have been added. These features should include, at a minimum, a polarizer, an analyzer, a rotatable circular stage, a cross-hair ocular, and a compensator slot. Quarter- and full-wave compensators should be part of the standard equipment. The most versatile of all for obtaining in-depth information from a sample, especially samples of transfer or trace evidence.
Polyacrylamide - A chemical used in the preparation of electrophoretic gels, these gels used for the separation of mixtures of macromolecules. A polymer that is used to separate relatively small DNA fragments. In forensic DNA analysis, used in AMP–FLP and STR analyses.
Polyester fiber A synthetic fiber of high tensile strength made by the esterification of ethylene glycol and other organic compounds.
Polyethylene terephthalate - A polyester formed from ethylene glycol by direct esterification or by catalyzed ester exchange between ethylene glycol and dimethyl terephthalate. Uses are: blended with cotton, for wash-and-wear fabrics, blended with wool for worsteds and suitings, packaging films,and recording tapes.
Polymer - A large molecule consisting of repeating units of a monomer. Polymers may be natural, such as cellulose, or synthetic, such as most plastics. A compound composed of many smaller subunits; results from the process of polymerization.
Polymerase - An enzyme believed to catalyze the formation of messenger DNA in the cell.
Polymerase chain reaction (PCR) - A technique in which cycles of denaturation,annealing with a primer, and extension with DNA Polymerase, are used to amplify the number of copies of a target DNA sequence more than a millionfold using thermal stable Taq Polymerase. Oligonucleotide primers must be annealed to the target DNA sequence 5′ flanking regions.The PCR may be likened to a molecular copy machine.
Polymorphic probe - A known DNA sequence that recognizes a specific locus on a chromosome that is polymorphic.
Polymorphism - Occurrence in a population of two or more genetically determined alternative phenotypes with frequencies greater than could be accounted for by mutation or drift. The occurrence of different forms,stages, or types in individual organisms, or in organisms of the same species, independent of sexual variation. In microchemistry, it is crystallization of a compound in at least two distinct forms.
Potassium chlorate (KClO3) - Transparent, colorless crystals or white powder;used as an oxidizing agent in explosives, matches, percussion caps, and textile printing.
Potassium ferricyanide (K3FeCN)6 - Bright red, lustrous crystals or powder.Used for tempering steel, etching liquid, production of pigments, electroplating,and fertilizer compositions.
Potassium nitrate (KNO3) - Transparent, colorless or white crystalline powder or crystals. Used in pyrotechnics, explosives, matches, metallurgy, and glass manufacture.
Potassium oxalate (K2C2O4•H2O) - Colorless transparent crystals, odorless, soluble in water and highly toxic if inhaled or ingested. Can be a strong irritant to tissue cells. Used to remove stains from textiles and photography.
Potassium perchlorate (KclO4) - Colorless crystals or white, crystalline powder.Decomposed by concussion, organic matter, and agents subject to oxidation.Used in explosives, medicine, oxidizing agents, photography, pyrotechnics,and flares.
Potassium permanganate (KMnO4) - Dark-purple crystals, with blue metallic sheen, sweetish astringent taste, and odorless. Used as an oxidizer, disinfectant,and deodorizer; for dye tanning, radioactive decontamination of skin; and as a reagent in analytical chemistry.
Precipitant - Any substance, as a reagent, that when added or applied to a solution results in the formation of a precipitate.
Precipitate - A substance separating in solid particles from a liquid as the result of a chemical or physical change.
Probe - A specific sequence of DNA that attaches to unzipped
DNA. A single-stranded segment of DNA, or mRNA, capable of being
tagged with a tracer, such as 32P, and hybridized to its complementary
Product gel - Diagnostic tool used in PCR analysis to determine if a DNA sample has been successfully amplified.
Pyridine - A colorless liquid, nitrogenous compound, C5H5N, with a pungent,noxious odor. Used in organic synthesis, as a disinfectant, antiseptic, and alcohol denaturant.
Pyrophoric distillation - The slow drying and passive pyrolysis of wood materials.
_Quantitative test - Chemical analysis to determine the amounts or concentrations of one or more components of a mixture.
Quantiblot - A slot blot technique that is used to obtain information about the quantity of human DNA extracted from evidence samples.
Radial fractures - Fractures that form a star shape when a bullet pierces a sheet of glass, and which originate on the side opposite to the initial impact._
Range - Concentration interval for which acceptable accuracy and precision can be achieved (adapted from). Statistically, it is the difference between the minimum and the maximum values of a set of measurements.
Reactivity - Ability of a substance to chemically interact with other substances.
Reagent blank control - This control consists of all reagents used in the test process minus any sample. This is used to detect DNA contamination of the analytical reagents and materials.
Reagent chemicals - High-purity chemicals used for analytical reactions, for testing of new reactions where the effect of impurities are unknown, and in general, for chemical work where impurities must either be absent or at a known concentration.
Reannealing - Spontaneous realignment of two single DNA strands to re-form a DNA double helix that had been denatured.
Reference material - Material or substance, one or more properties of which are sufficiently well established to be used for calibrating an apparatus, assessing a measurement method, or assigning values to materials.
Reference method or standard consensus method - Method developed by organizations or groups that use collaborative studies or similar approaches to validate a new method or a new instrument. A method’s value depends on the authority of the organizations that sponsor it.
Reference shoes - Shoes known to belong to an individual that are used as a known comparison standard in a barefoot comparison.
Reference standard - A standard, generally of the highest quality available at a given location, from which measurements made at that location are derived.
Reflection - The bouncing back of rays of light striking a surface.
Refraction - The bending of a light ray when passing obliquely from one medium to a medium of different density.
Renaturation - The reassociation of denatured complementary single strands of a DNA double helix. The restoration of the DNA molecule back to its double helix form. Repeating unit in a tandem cluster is the length of the sequence that is repeated and appears circular on a restriction map.
Resolution - (Chromatography) A measure of the separation of components; in thin-layer chromatography (TLC), the ability to visually separate spotted drug samples on a glass plate. (Spectroscopy) A measure of the ability of the instruments to detect individual absorbance peaks.
Retention index - In gas chromatography, the relationship of retention volume with arbitrarily assigned numbers to the compound being analyzed, used to indicate the volume retention behavior during analysis.
Retention time - The length of time required for a compound or component of a mixture to pass through a chromatographic column.
Saliva - Oral secretion comprised of water, mucus, proteins, salts, and enzymes.Its primary functions are to moisten the mouth, lubricate chewed food,and aid in digestion.
Scale - The enlargement or reduction of an object or texture.
Satellite spatter - Small droplets of blood that are projected around or beside a drop of blood upon its impact with a surface. A wave castoff is also considered a form of satellite spatter.
Scallop pattern - A bloodstain produced by a single drop that is characterized by a wave-like, scalloped edge.
Scanning electron microscope (SEM) - A microscope that is used to study the surface morphology of different types of samples. The images produced are striking and often give the illusion of being three dimensional. A microscope that utilizes an accelerated focused electron beam to image particulate samples (e.g., gunshot residue) at high magnification, with great depth-of-field, while providing size, shape, morphology, and chemical information in both manual and automated modes.
Scent cone - The patterned distribution of scent molecules that have diffused from a source, generally becoming less concentrated and more dispersed the further they diffuse from the source.
Schlieren optics - Imaging system in which the transparent or translucent object to be examined is placed between two spherical mirrors.
Secondary contamination - Transfer of a harmful substance from one body (primary body) to another (secondary body), thus potentially permitting adverse effects to the secondary body.
Secretor - An individual whose genetic markers can be detected by using their saliva and testing for a polymorphic antigen that adheres to the cell surfaces, such as in the Lewis system.
Selenium - Nonmetallic element sensitive to light; used as a coating on drums of photocopying machines.
Selvage - The narrow edge of woven fabric that runs parallel to the wrap. It is made with stronger yarns in a tighter construction than the body of the fabric to prevent raveling.
Semen - Sperm cells plus the seminal fluid. Complex mixture of organic and inorganic substances produced in the postpubertal male genital tract. The term semen is applied to the fluid that is ejaculated.
Serologist - An individual who, through their examination of evidence, characterizes and identifies blood and body fluids.
Serology - The science of serums and their actions.
Serum - The watery, straw-color fluid that separates from blood on coagulation.
Serum stain - A clear, yellowish stain with a shiny surface often appearing around a bloodstain after the blood has retracted due to clotting. The separation is affected by temperature, humidity, substrate, and air movement.
Sex chromosomes (X and Y chromosomes) - Chromosomes whose contents are different in the two sexes, usually labeled X and Y; the male species has the XY chromosomes and the female species has the XX chromosomes.In DNA profiles these chromosomes are referred to as amelogenin.
Shoe print -A two-dimensional impression of a shoe. A shoe mark.
Skeletonization - Removal of soft parts of the body, leaving only the skeleton.
Skeletonized bloodstain - A bloodstain that consists only of its outer periphery,the central area having been removed by wiping after liquid blood has partially dried. A skeletonized bloodstain is also produced by the flaking away of the central portion of a completely dried stain.
Skewness - Said of measures or scores that are bunched on one side of a central tendency parameter (mean, median, mode) and trail out on the other. The more skewness in a distribution, the more variability in the scores. Also used to refer to asymmetry in, for example, a chromatographic peak shape (“tailing” and “fronting”).
Sloughing - Process by which necrotic cells separate from the tissue to which they have been attached.
Smear - A relatively large volume of blood, usually 0.5 ml or more, that has been distorted to such a degree that further classification is not possible. A smear is similar to a smudge, but a smear is a stain produced by a large volume of blood.
Snow Print Wax - Registered name of an aerosol product used to assist in the photography and casting of footwear impressions in snow.
Sodium fluoride and potassium oxalate - Chemicals found inside a gray-top test tube; the sodium fluoride prevents bacterial growth and the potassium oxalate binds the calcium in the blood, which prevents blood from clotting.These chemicals are in gray-stopper vacutainer tubes used when testing for alcohol in the blood.
Solubility - Ability of one material to dissolve in or blend uniformly with another.
Solute - In thin-layer chromatography, a mixture of components to be separated.The substance dissolved in a solvent.
Solution - A single, homogeneous liquid, solid, or gas phase that is a mixture in which the components (liquid, gas, or solid) are uniformly distributed throughout the mixture.
Solvent - Organic liquids of various types having the function of dissolving the binder and thereby providing a consistency to the coating that is more suitable for application.
Solvent front - The final point reached by the mobile phase as it flows up or across the thin-layer chromatography plate during development of the chromatogram.
Spatter - The dispersion of small blood droplets due to the forceful projection of blood.
Specific gravity - The ratio of the mass of a unit volume of a substance to the mass of the same volume of a standard substance (usually water) at a standard temperature.
Spectrometer - Photometric device for the measurement of spectral transmittance,spectral reflectance, or relative spectral emittance. An instrument used to measure the intensity of a specific wavelength of light entering and leaving a solution.
Spectrophotometer - An instrument used to measure the intensity of a specific wavelength of light entering and leaving a solution. A light-measuring device, which incorporates a monochrometer to isolate and project particular wavelengths of electromagnetic radiation through a sample, and a detector to measure the amount of radiation that has passed through the sample.
Spectroradiometer - A form of spectrometer for determining the distribution of the intensity of any type of radiation, especially in the infrared region of the spectrum.
Spectroscopy - Observation by means of an optical device (spectroscope) of the wavelength and intensity of electromagnetic radiation (light) absorbed or emitted by various materials.
Spectrum - A colored band formed when white light is passed through a prism.
Sperm (cell) fraction - In a differential extraction, the portion of a sample containing DNA from the sperm cells.
Spermatozoa - (sperm cell) A male reproductive cell. The male fertilizing element of an animal, usually in the form of a nucleated cell with a long flagellate process or tail by which it swims actively about.
Spherulites - Spheres composed of needles or rods, all oriented perpendicular to the outer surface, or a plane section through such a sphere. A common form of polymer crystallization from melts or concentrated solutions.
Spike - A peak in an electropherogram caused by electrical fluctuations in the current.
Spine - The pointed-edge characteristics that radiate away from the center of a bloodstain.Their formation depends upon impact velocity and surface texture.
Spinneret - (1) One of the organs perforated by tubes connected with glands secreting liquid silk, as in spiders. (2) A metal plate pierced with holes through which filaments of plastic material are forced, as in the making of rayon fibers.
Splash - A stain pattern created by a low-velocity impact upon a quantity of blood approximately 0.10 ml or greater striking the surface.
Spot - A round zone of sample application at the origin; in a thin-layer chromatography plate, a round zone caused by migration of a component of the solute.
Spotting - Applying a solute sample at the origin of the thin-layer chromatography plate.
Stability - Resistance to decomposition or other chemical changes, or to physical disintegration.
Stain - A solution of a dye or a suspension of a pigment in a vehicle
designed to impart a color to wood surface rather than to form a protective coating.
Stage micrometer - A microscope slide with a scale usually divided into 10-mm or 0.001-in. units. It is used to calibrate the eyepiece scale of a microscope used for measuring.
Standard addition - The addition of a known amount of a pure component supposed to be present as a constituent of the specimen or sample in order to verify and quantitate this component. Operationally, a measurement is made on the specimen or sample, a known amount of the desired constituent is added, the modified specimen or sample is remeasured, and the amount of the constituent originally present is determined by proportionation.
Standard deviation (SD) - A statistic that shows the spread or dispersion of scores in a distribution of scores. It is calculated by taking the square root of the variance. It is applicable to all kinds of repeated measurements,e.g., between-batch, within-batch, repeatability, and reproducibility.
Standard operating procedures (SOP) - Written procedures that describe how to perform certain laboratory activities.
Standards - A condensed and compact set of authentic specimens which, if adequate and proper, should contain a true cross section of the material from a known source.
Starch-gel electrophoresis - A method that uses purified starch-gel as a support medium to hold proteins while they are separated in an electric field.
Stasis change - Stoppage of the blood in its circulation, especially in the small vessels and capillaries; caused by abnormal resistance of the capillary walls, rather than by any lessening of the heart’s action.
Stationary phase - The solid adsorbent coating layer on thin-layer chromatography plates. In a packed column, the stationary phase is a low vapor pressure liquid that coats a solid support. Compounds are selectively retained based on their solubility in this liquid. In a capillary column, the stationary phase is generally a modified or unmodified polysiloxane compound coating the walls of a fused silica column. Compounds are selectively retained based on their interaction with the coating’s functional group.
Stereo binocular microscope Two similar but separate optical microscopes for observation by both eyes simultaneously for low to medium magnification in the range of 4 to 40 times.
Stereoisomers - Compounds with identical structural formulas; they differ in the way their molecules are arranged.
Stereomicroscope - An instrument for blending into one image two pictures of an object from slightly different points of view so as to produce upon the eye the impression of relief and solidity. This type of microscope provides a three-dimensional image.
Sterile technique - A procedure that aids in the elimination of contamination with the use of gloves, sterile supplies, and a clean working area, as well as the frequent change of pipette tips for each reagent addition to each reaction tube.
Steroid - One of a group of polycyclic compounds closely related biochemically to terpenes.
Stitching - Characteristic marks left by a tool used when joining the various unvulcanized rubber parts of a shoe together prior to vulcanizing. It is associated primarily with shoes made utilizing unvulcanized rubber soles,foxing strips, and rubber upper components. Also, the application of thread through the bottom (bottom stitched) or side (side stitched) of a shoe to help join the outsole to the upper.
Stock solution - Concentrated standard solution used to prepare calibrators.
STR (short tandem repeat) - Also referred to as microsatellites. An elementary form of repetitive DNA that occurs in mammalian genomes, determined by di-, tri-, and tetra-nucleotide repeats arranged in very short arrays.
Strand - A single fiber, filament, or monofilament.
Stratification The actual observable sequential layering of soil, rocks, or surface debris.
Swipe, smear - (bloodstain) The transfer of blood onto a surface not already contaminated with blood. One edge is usually feathered, which may indicate the direction the blood traveled.
Synthetic fibers - A class of manufactured polymeric fibers that are synthesized from a chemical compound (e.g., nylon, polyester).
Technical fiber - A bundle of natural fibers composed of individual elongated cells that can be physically or chemically separated and examined microscopically for identifying characteristics (e.g., hemp, jute, and sisal).
Telogen - A quiescent phase in the cycle of hair growth when the hair is retained in the hair follicle as a dead or “club” hair. The dormant or resting phase of hair growth. Hair in the telogen phase is shed naturally.
Terminal velocity - The maximum speed to which a free-falling drop of blood can accelerate in air, approximately 25.1 ft/sec.
Test impression - An impression made utilizing a known shoe for the purpose of using it in a footwear impression examination.
Test linearity - Ability within a given range to obtain test results directly proportional to the concentration (amount) of analyte in the specimen or sample.
Test mark - A striated or impressed tool mark produced by the suspect tool,which is to be used in making a comparison with the evidence mark.
Texture - A rough surface of shallow design added to a mold through a stippling or a chemical etching process. Texture patterns vary in their position and features and are unique to a mold. The texture is reproduced in shoes made in that mold.
Thermal conductivity detector - A type of gas chromatographic detector that is sensitive to the change in the ability of the gases emerging from the column to conduct heat. A thermal conductivity (TC) detector is not as sensitive as a flame ionization detector, but is capable of detecting some molecules, such as water, which give no signal on FID.
Thermocycler - An instrument that is programmed to heat and cool automatically.This instrument is used to carry out the PCR steps in DNA amplification.
Thermolabile - Decomposed, destroyed, affected, or liable to be adversely affected by heat, as in some enzymes and toxins.
Thermoplastic fiber - A synthetic fiber that will soften or melt at high temperatures and harden again when cooled.
Thin-layer chromatography (TLC) - A procedure for separating compounds by spotting them on a glass plate coated with a thin (about 0.01 in.) layer of silica or alumina and “developing” the plate by allowing a solvent to move upward by capillary action. TLC is especially useful for identifying and comparing materials that are highly colored or which fluoresce under ultraviolet light. TLC is used extensively in explosive analysis and in the comparison of gasoline dyes, inks, and various drugs.
Threshold - (cut-off concentration) A particular, significant amount, level, or limit, at which something begins to happen or take effect.
Tint - A color that has been made lighter by the addition of white.
Titer - The concentration in a solution of a dissolved substance as shown in titration. The least amount or volume needed to give a desired result in titration.
Titrate - To make a series of dilutions.
Titration - A method of analyzing the composition of a solution by adding known amounts of a standardized solution until a given reaction (color change,precipitation, or conductivity change) is produced.
TNT - (trinitrotoluene) A high explosive used as a component of some priming mixtures.
Toluene - (methylbenzene) An aromatic compound having the formula
C6H5CH3. It is a major component of gasoline. Toluene has a flash point
of 40°F and explosive limits of 1.2 to 7%.
Tongue - A strip of material covering the instep of the foot, lying beneath the shoe laces.
Tool-mark identification - A discipline of forensic science that has as its primary concern the determination if a tool mark was produced by a particular tool.
Transfer pattern - A contact bloodstain created when a wet, bloody surface contacts a second surface. A recognizable mirror image or at least a recognizable portion of the original surface may be transferred to the second surface.
Transfer theory - The theory attributed to Edmond Locard regarding the transfer of trace evidence between two objects.
Triacetate fiber - Generic name for a manufactured fiber in which the fiberforming substance is cellulose acetate, where not less than 92% of the hydroxyl groups are acetylated. The term triacetate may be used as a generic description of the fiber.
Tungsten - Metallic element, atomic number 74, hard brittle, gray solid. Has high electrical conductivity. Used in high-speed tool steel, as filaments for electric light bulbs, and as heating elements in furnaces and vacuummetallizing equipment.
Tungsten light - Incandescent light, from a bulb having filaments usually of lower wattage, 15 to 500 W.
Turpentine - (1) Gum form — the pitch obtained from living pine trees; a sticky viscous liquid. (2) Oil form — a volatile liquid obtained by steam distillation of gum turpentine, consisting mainly of pinene and diterpene.
Turpentine is frequently identified in debris samples containing burned
wood from arson cases.
Twine - A string composed of two or more strands twisted together.
Two-dimensional impression - (1) An impression that for all practical purposes has the dimensions of length and width but not a significant depth. (2) A shoe mark.
Thermoplastic polymer - A resin that polymerizes without the necessity of heat. If the resin is heated below its decomposition temperature it softens and hardens again upon cooling; hence, the term thermoplastic.
Thermosetting polymer - A resin that can be made to form cross-linkage when baked.
Ultraviolet - Radiation in the region of the electromagnetic spectrum including wavelengths from 100 to 380 nm.
Ultraviolet examination - Ultraviolet radiation is invisible and occurs in the wavelengths just below the visible blue-violet end of the spectrum. The invisible rays react on some substances so that visible light is emitted, a phenomenon known as ultraviolet fluorescence. Thus, ultraviolet examination may be made visually or photographically by recording either the reflected ultraviolet or visible radiation.
Ultraviolet filter - A filter that transmits ultraviolet light as used for photography by the reflected ultraviolet light method.
Ultraviolet light - Light rays beyond the visible spectrum of light at its violet end with wavelengths longer than x-rays, but shorter than visible light.
Ultraviolet spectrometer - A device that produces a spectrum of ultraviolet light and is provided with a calibrated scale for measurement of wavelength.
Uniaxial - With one axis, movement only in one plane, as that of hinge-joint.
Urea - A protein denaturant, urea is qualified for use as the denaturing component in polyacrylamide gels.
Urine - Liquid produced in the kidneys; contains biological waste
Urobilinogen - Intermediate product in the metabolism of bilirubin. When combined with zinc acetate, it forms a compound that fluoresces in ultraviolet light; used for the identification of feces.
Validated method - Method whose performance characteristics meet the specifications required by the intended use of the analytical results. Some of the performance characteristics to be evaluated are limit to detection, limit of quantitation, linearity, precision, range, ruggedness, selectivity and specificity, and trueness.
van der Waal’s forces - Weak attractive forces acting between molecules. They are involved in the van der Waals equation of state for gases that compensates for the actual volume of the molecules and the forces acting between them.
Vanillin - The methyl ether of protocatechute aldehyde, occurring in vanilla bean extract and in many balsams and resins.
Velvet - A fabric with a short, thick-set pile of silk, cotton, or other fiber on a back that is closely woven and of the same or different fibers.
Vermiculite - A micaceous hydrated silicate mineral used as a planting medium and as insulation.
Vernier caliper - A measuring instrument having a fixed jaw and a sliding jaw with an attached vernier.
Viscosity - The internal resistance to flow exhibited by a fluid.
Void or shadow - Absence of bloodstain in an otherwise continuous bloodstain pattern. Often the geometry of the void will suggest an outline of the object that has intercepted the blood, such as a shoe, furniture, person,etc.
Volumetric flask - A laboratory flask primarily intended for the preparation of definite, fixed volumes of solutions.
Vulcanization - An irreversible process in which a rubber compound is heated under pressure, resulting in a chemical change in its structure. The process to which shoes with raw rubber components are subjected in order to permanently bond the components together.
Varnish - A homogenous solution of drying oils and resins in organic solvents.The resins may be naturally occurring, such as rosin or dammar, or synthetic.
Vehicle - The portion of a surface coating other than the pigment, the purpose of which is to enable the pigment to be distributed over the surface. The vehicle includes solvents, binders, and other additives. The term vehicle is frequently used to indicate the oil or resin that forms a continuous film and binds the pigment to the substrate.
Wagner’s reagent - An aqueous solution of iodine and potassium iodide; used for microchemical analysis of alkaloids. Also known as Wagner’s solution.
Wale - A column of loops lying lengthwise in a knit fabric.
Walker test - The original chemical test for the detection of the spatial distribution of nitrites in gunpowder residue.
Warp - The set of yarn in all woven fabrics that runs lengthwise and parallel to the selvage and is interwoven with the filling.
Watson and Crick model - Refers to the DNA molecule that forms a doublehelix ladder with the complementary strands held by hydrogen bonds between specific base pairs.
Wave, castoff - A small blood droplet that originates from a parent drop of blood due to the wavelike action of the liquid in conjunction with striking a surface at an angle less than 90°.
Wavelength - The distance, measured along the line of propagation, between two points that are in phase on adjacent waves. A property of radiant energy,such as IR, visible, or UV.
Wear - The erosion of the outsole due to frictional and abrasive forces that occur between the outsole and the ground. Effect of frictional forces on a tire or shoe; wear eventually changes the design.
Weft (filling) - In a woven fabric, the yarn running from selvage to selvage at right angles to the wrap.
Wet origin impression - Footwear impression containing significant moisture from the shoe sole or substrate.
Wipe - A bloodstain pattern created when an object moves through an existing bloodstain, removing blood from the original stain and altering its appearance.
Wood’s lamp - Light source used by physicians to detect various substances,including semen stains. It may be used in cases of suspected child sexual maltreatment.
Woven fabric - Generally used to refer to fabric composed of two sets of yarns,wrap and weft (filling), formed by weaving, which is the interlacing of these sets of yarns.
X-chromosome - A chromosome responsible for sex determination. Two copies are present in the genome of the homogametic sex and one copy in the heterogametic sex. The human female has two X-chromosomes and the male has one X-chromosome.
X-ray diffraction - An analytical technique used to identify crystalline solids by measuring the characteristic spaces between layers of atoms or molecules in a crystal. X-ray diffraction can be very useful in the identification of explosive residue.
X-ray fluorescence emission spectrometer - An x-ray crystal spectrometer used to measure wavelengths of x-ray fluorescence in order to concentrate beams of low intensity. It has bent reflecting or transmitting crystals arranged so that the theoretical curvature required can be varied with the diffraction angle of a spectrum line.
X-rays - Electromagnetic radiation of high energy and very high frequency that can penetrate most materials to different extents and reveal their underlying structures.
Xylotomist - An expert in the study of wood.
Y-chromosome - A chromosome responsible for sex determination in the heterogametic sex. This occurs in the male (XY) mammals.
Yield gel - The mobility of the undigested DNA indicates the quality of the isolated DNA. Undigested DNA is applied to a 15-cm agarose gel, size separated by electrophoresis, and stained with ethidium bromide. The purpose of this gel is to aid in assessing the amount of total DNA recovered from a forensic sample, as well as the state of degradation of the DNA.