DNA.gov > Glossary

Glossary

#'s : A : B : C : D : E : F : G : H : I : J : K : L : M : N : O : P : Q : R : S : T : U : V : W : Y

2p rule: The NRCII report recommends using this approach for dealing with homozygotes.
A.F.I.S.: Automated Fingerprint Identification System
ABO blood typing: A commonly used genetic typing test that uses antibodies to detect variations on the surface of human red blood cells. Individuals are typed as having A, B, O, or AB type blood by testing liquid or stains from body fluids (e.g., blood, saliva, vaginal secretions). One out of every three randomly selected pairs of people have the same ABO blood type.
Adenosine Triphosphate (ATP): Main source of energy for biochemical reactions within the cell.
Allele: A different form of a gene at a particular locus. The characteristics of a single copy of a specific gene, or of a single copy of a specific location on a chromosome. For example, one copy of a specific short tandem repeat (STR) region might have 10 repeats, while the other copy might have 11 repeats. These would represent two alleles of that STR region.
Allele Frequencies: Term used to characterize genetic variation of a species population.
Allelic dropout: Failure to detect an allele within a sample or failure to amplify an allele during PCR.
Allelic ladder: Comprised of DNA fragments that represent common alleles at a locus.
Alternate light source (ALS): Equipment used to produce visible and invisible light at various wavelengths to enhance or visualize items of evidence (fluids, fingerprints, clothing fibers, etc.). The light will cause possible biological stains to change color or fluoresce, assisting in the location process.
Alu: Non-coding regions of DNA containing a restriction site for the enzyme Alu 1. The sequences are about 300 base pairs long and are repeated several thousand times throughout the genome.
Amelogenin: A gene present on the X and Y sex chromosomes that is used in DNA identification testing to determine the gender of the donor of the DNA in a biological sample.
Amorphous medulla: An amorphous medulla has no distinct form, pattern, or shape when viewed with a transmitted light microscope
Amplicons: Amplified DNA fragments.
Amplification: Producing multiple copies of a chosen DNA region, usually by PCR (Polymerase Chain Reaction).
Amplified Fragment Length Polymorphisms (AFLP or AmpFLP): A highly sensitive method for detecting polymorphisms in DNA. DNA first undergoes restriction enzyme digestion, and a subset of DNA fragments is then selected for PCR amplification and visualization.
Anagen: The anagen root is the active growth phase of a hair follicle in the hair growth cycle
Analytical Threshold: An acceptable "Relative Fluorescence Units" (RFU) level determined to be appropriate for use in the PCR/STR DNA typing process. A minimum threshold for data comparison is identified by the specific forensic laboratory doing the testing through independent validation studies.
Angular aperture: The angle (or cone) of light rays capable of entering the front lens of the objective from a point in the object. If the angular aperture of an objective is increased, more light rays from the specimen can be taken in by the lens, increasing the resolving power.
Annealing Temperature T_a: An annealing temperature is approximately 5°C below the lowest melting temperature Tm of the pair of primers used.
Anode: A positively charged electrode.
Artifact: Any non-allelic product of the amplification process (Stutter or Minus A) or anomaly of the detection process (Pull-up or Spike).
ASCLD: American Society of Crime Lab Directors
ASCLD-LAB: The American Society of Crime Lab Directors – Laboratory Accreditation Board. ASCLD-LAB is a crime lab accreditation program organized to review and inspect the quality assurance of forensic laboratories and insure that specified standards are followed. Accreditation is only available to forensic laboratories that perform casework.
Autosomal: Chromosomes which are not sex chromosomes.
Base Pairing: A,T,C and G are molecular building blocks of DNA that only continue in specific "base" pairs, e.g.,A only pairs with T, and C only pairs with G
Baseline: Residual signal associated with an instrument's blank response.
Bases: The four building blocks of DNA are called bases. The building blocks are Cytosine, Guanine, Thymine, Adenine and are commonly referred to as C, G, T, A.
Bayesian probability: System of probability based on beliefs in which the measure of probability is continuously revised as available information changes.
Bench notes: A laboratory analyst's recorded notes.
Biallelic: Pertaining to both alleles, e.g. single nucleotide polymorphisms display two alternate forms and are biallelic.
Bindle paper: Clean paper folded for the containment of trace evidence, sometimes included as part of the packaging for collecting trace evidence.
Biohazard bag: A container for materials that have been exposed to blood or other biological fluids and have the potential to be contaminated with hepatitis, AIDS, or other contagions.
Biological Evidence: Evidence commonly recovered from crime scenes in the form of hair, tissue, bones, teeth, blood or other bodily fluids.
Biological fluids: Fluids that have human or animal origin, most commonly encountered at crime scenes (e.g., blood, mucous, perspiration, saliva, semen, vaginal fluid, and urine).

Blind testing: In a blind test, analysts do not know they are being tested. In most forensic DNA laboratories, blind tests are not used.

In practice, it is almost impossible to design and implement an effective blind PT (proficiency test) program in forensic science. Most attempts have failed because they could not produce an effective case scenario with realistic representation of the pre-laboratory steps. Others failed because the analyst recognized that the supposed "evidence" was a manufactured artifact. Overall, it has proven impossible to realize the theoretical extra benefits of blind testing, and resources have been devoted to promoting better quality external open tests.

Bloodborne Pathogens: Disease-causing microorganisms that are present in blood and can cause disease in humans. Pathogens include, but are not limited to, hepatitis B virus (HBV) and human immunodeficiency virus (HIV).
Boundaries: The perimeter or border surrounding potential physical evidence related to the crime.

Bovine serum albumin (BSA): Protein fraction of serum isolated from the bovine family (i.e. cow, ox, buffalo).

Buckling: Buckling is a disruption of the hair shaft demonstrating itself as an abrupt change in direction with or without a slight twist. This feature may be due to genetic factors, or it may result from damage (i.e., hair treatments).

Buffer: Chemical solution that maintains a relatively constant pH even with the addition of strong acids or bases.
Cambridge Reference Sequence (CRS): A "master template" of the HVR-1 region of mitochondrial DNA.
Cambridge Reference Sequence, revised (rCRS): The rCRS sequence is a modified version of the original Cambridge Reference Sequence (GenBank #J01415.0 gi:337188) of Anderson et al (1981).
Capillary Electrophoresis (CE): The platform for CE uses narrow silica capillaries (or tubes) containing a polymer solution through which the negatively charged DNA molecules migrate under the influence of a high voltage electric field. Important advantages of the CE technique, compared to slab gel electrophoresis, include quicker and more easily automated analyses
Cartilage Hair Hypoplasis: A hair disorder that results in abnormally fine, sparse, and lightly colored hair that is usually short.
Case file: The collection of documents comprising information concerning a particular investigation. (This collection may be kept in case jackets, file folders, ring binders, boxes, file drawers, file cabinets, or rooms. Sub-files are often used within case files to segregate and group interviews, media coverage, laboratory requests and reports, evidence documentation, photographs, videotapes, audiotapes, and other documents.)
Case Identifier: The alphabetic and/or numeric characters assigned to identify a particular case.
Catagen: The catagen phase is the transitional phase of the hair follicle from the active growth phase (anagen) to the resting growth phase (telogen) in the hair growth cycle.
Cathode: A negatively charged electrode.
Cation: Positively charged ion. (e.g., K⁺, Na⁺, NH4⁺)
Caucasoid: Caucasoid is an archaic anthropological term designating the peoples originating from Europe and the Indian subcontinent.
Cell: The smallest component of life capable of independent reproduction and from which DNA is isolated for forensic analysis.
Central Distribution (pigment): The distribution and concentration of the pigment in the center of the cortex.
Chain of Custody: A record of individuals who have had physical possession of the evidence and the process used to maintain and document the chronological history of the evidence. (Documents can include, but are not limited to, name or initials of the individual collecting the evidence; each person or entity subsequently having physical possession of it; dates the items were collected or transferred; from where the item(s) were collected; agency and case number; victim's or suspect's name (if known); and a brief description of the item.)
Chaotropic: Property of certain substances to disrupt the structure of water. Promotes the solubility of non-polar substances and the elution from or movement through a chromatographic medium of an otherwise tightly bound substance.
Chemiluminescence: The release of light (photons) as the result of a chemical reaction.
Chi-squared Test of Association: Comparison of the observed frequencies with the frequencies that would be expected if the null hypothesis of no association were true.
Chloroform: A chemical used in organic extraction. When used with phenol, promotes a sharp interface between the organic and aqueous layers.
Chromosome: The biological structure by which hereditary information is physically transmitted from one generation to the next. Located in the cell nucleus, it consists of a tightly coiled thread of DNA with associated proteins and RNA. The genes are arranged in linear order along the DNA.
Clean/sanitize: The process of removing biological and/or chemical contaminants from tools and/or equipment.

CODIS Combined DNA Index System: A collection of databases of DNA profiles obtained from evidence samples from unsolved crimes and from known individuals convicted of particular crimes. Contributions to this database are made through State crime laboratories and the data are maintained by the FBI. Learn more about CODIS on the FBI's Web site.
CODIS core loci: Thirteen STR (short tandem repeat) sequences that have been selected for the Combined DNA Index System (CODIS).
Cold hit: When CODIS recognizes a match between an offender and forensic profile, it is referred to as a "cold hit."
Collect/collection: The process of identifying, documenting, gathering, and packaging or retaining physical evidence.
Combined Paternity Index (CPI): Odds ratio that depicts the likelihood of the alleged father being the biological father, in comparison to the likelihood of a random unrelated man in the population being the biological father.
Comparison microscope: Two microscopes joined by an optical bridge to present a split-view, side-by-side comparison of two specimens; for example, two hairs on separate slides.
Competency: The combination of demonstrated knowledge, skills, and abilities.
Competency Test: A test given during training to assess the ability of a trainee.
Concave: Lenses or mirrors which bow in.
Confidence Interval: Estimated range of values (calculated from a given set of sample data) that is likely to include an unknown population parameter.
Confirmatory Test: A simplistic method for estimating genotype frequency by direct counting of the number of times a genotype is observed in a database.
Contamination: The undesirable transfer of material to physical evidence (DNA) from another source.
Continuous (medulla): A form of hair medullation where the visible medulla extends uninterrupted along a length of hair shaft.
Control Samples: Cuttings, swabbings, etc., from unstained adjacent material. A control sample is material of a known source that presumably was uncontaminated during the commission of the crime (e.g., a sample to be used in laboratory testing to ensure that the surface on which the sample is deposited does not interfere with testing. For example, when a bloodstain is collected from a carpet, a segment of unstained carpet must be collected). The control sample should be taken adjacent to the biological stain being collected.
Controls: Tests designed to demonstrate that a procedure worked correctly and performed in parallel with experimental samples.
Convex: Lenses or mirrors that bow out.
Convolution: A convolution is an abrupt rotation of the hair shaft that can occur naturally, from disease, or as a result of mechanical force.
Cortex: The cortex is the primary anatomical region of a hair between the cuticle region and the medullary region composed of elongated and fusiform cells.
Cortical Fusi: Cortical fusi are the small spaces within the hair shaft that appear as microscopic dark structures, commonly at the proximal end of hairs; they can be filled with air or liquid.
Cross Contamination: The undesirable transfer of material between two or more sources of physical evidence.
Cross Projection Sketch: Also commonly referred to as an Exploded View Sketch. This type of sketch views the scene from above similar to a Birds-eye View but with the walls folded down. This sketch is used to show evidence on the walls such as blood spatter and bullet holes.
Cross-sectional shape: The cross-sectional shape is the shape of a hair shaft cut and viewed at a right angle to its longitudinal axis.
Curled: A hair shaft form that is bent into or towards a spiral form.

Curved: A hair shaft form with slight curvature but does not exhibit waviness or does not curl back upon itself to form a circle.
Cuticle: The cuticle is the outermost region of a hair and is composed of layers of overlapping scales.
Cycle Threshold (CT): Cycle number (in qPCR) at which the fluorescence generated within a reaction well exceeds the defined threshold. The threshold is arbitrarily defined by the manufacturer to reflect the point during the reaction at which a sufficient number of amplicons have accumulated.
Cytoplasm: The viscid, semifluid matter contained within the plasma membrane of a cell, excluding the nucleus.
Degenerate Primer: A PCR primer sequence is called degenerate if some of its positions have several possible bases.
Degradation: The fragmenting, or breakdown, of DNA by chemical or physical means.
Denaturation: Separation of the two strands of a DNA double helix.
Deposition: The taking and recording of testimony of a witness under oath before a court reporter in a place away from the courtroom before trial.
Depth of field: Axial resolving power of an objective, which is measured parallel to the optical axis.
Depth of focus: The range of distances between a lens and image plane for which the image formed by the lens at a given setting is clearly focused. With a high numerical aperture microscope objective, the depth of field is very shallow, but the depth of focus can be quite deep and reach several millimeters.
Dermal papilla: Connective living tissue from which hair is generated from the follicle in the thick layer of the skin below the epidermis
Dideoxy sequencing: Dideoxynucleotide sequencing, also known as the "Sanger method," is a technique which uses dideoxyribose instead of deoxyribose to stop the synthesis of a complementary DNA strand at various points when sequencing.

Differential extraction: A procedure in which sperm cells are separated, or extracted, from all other cells in a sample.
Diffuse Light: light reflected uniformly in all directions regardless of what angle the light comes in at.
Discontinuous (medulla): A form of hair medullation where the visible medulla is interrupted or fragmented along a length of hair shaft.

Discriminating Power: The ability of a blood grouping technique to differentiate between individuals selected at random. This can also be applied to other analytical techniques in forensic science.
Disposable instruments: Items that will be used only once to collect evidence, such as biological samples, then discarded to minimize contamination (e.g., tweezers, scalpel blades, droppers).
Dissimilar: Not similar or alike; different in appearance, properties, or nature; unlike.
Distal End: The end of the hair away from the root; towards the tip.
Dithiothreitol (DTT): Reducing or deprotecting agent for thiolated DNA. (1,4-Dicaptomercapto-2,3-butanediol; formula is C4H10O2S2)
DNA (Deoxyribonucleic acid): Often referred to as the "blueprint of life," DNA is the genetic material present in the nucleus of cells which is inherited half from each biological parent. DNA is a chemical substance contained in cells, which determines each person's individual characteristics. An individual's DNA is unique except in cases of identical twins.
DNA Analysis: The process of testing to identify DNA patterns or types. In the forensic setting, this testing is used to exclude or include individuals as possible sources of body fluid stains (blood, saliva, semen) and other biological evidence (bones, teeth, hair). This testing can also be used to indicate parentage.
DNA fingerprinting: Analyses of the lengths of the fragments reveal that when looking at multiple VNTRs (variable number of tandem repeats) within and between individuals, no two people have the same assortment of lengths. This technique became known to the public as "DNA fingerprinting"because of its powerful ability to discriminate between unrelated individuals.
DNA mixtures: A sample that contains the DNA of more than one individual.
DNA Profile: The result of determining the relative positions of DNA sequences at several locations on the molecule. Each person (except identical twins) has a unique DNA profile when used in the context of the CODIS database, which evaluates 13 specific DNA locations.
Documentation: Written notes, audio/videotapes, printed forms, sketches, and/or photographs that form a detailed record of the scene, evidence recovered, and actions taken during the search of the crime scene, including chain of custody information.
Double Helix: The shape the DNA assumes after it replicates during cell life.
Electropherogram: The graphic representation of the separation of molecules by electrophoresis or other means of separation.
Electrophoresis: A method of separating large molecules (such as DNA fragments) from a mixture of similar molecules. An electric current is passed through a medium at a different rate, depending on its electrical charge and size. Separation of DNA markers is based on these differences.
Elimination/Reference samples: A term used to describe a sample of known source taken for comparison purposes.

Example-An elimination sample is one of known source taken from a person who had lawful access to the crime scene (e.g., blood or cheek [buccal] swabs for DNA analysis, fingerprints from occupants, tire tread impressions from police vehicles, footwear impressions from emergency medical personnel) to be used for comparison with evidence of the same type.

A reference sample is material of a verifiable/documented source which, when compared with evidence of an unknown source, shows whether an association or linkage exists between an offender, crime scene and/or victim (e.g., a carpet cutting taken from a location suspected as the point of transfer for comparison with the fibers recovered from the suspect's shoes, a sample of paint removed from a suspect's vehicle to be compared with paint found on a victim's vehicle following an accident, or a sample of the suspect's and/or victim's blood submitted for comparison with a bloodstained shirt recovered as evidence).
Ethnicity: Property of a culture or subculture whose members are readily distinguishable based on traits originating from a common source (e.g. racial, national, linguistic, etc.). Members of an ethnic group are often presumed to be culturally or genetically similar; this is not necessarily true.
Evidence: Something that can help identify the responsible persons, establish an element of crime, reconstruct crime events or link crimes.
Evidentiary 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.
Excluded: Two samples cannot have come from the same source.
Exclusion: A DNA test result indicating that an individual is excluded as the source of the DNA evidence. In a criminal case, "exclusion" does not necessarily equate to "innocence." This occurs when one or more types from a specific location in the DNA of a known individual are not present in the type(s) for that specific location in the DNA obtained from an evidence sample.
Exogenous DNA: DNA originating outside an organism that has been introduced into the organism.
Exonuclease: An enzyme that cleaves nucleotides one at a time from an end of a polynucleotide chain. An enzyme that hydrolyzes phosphodiester bonds from either the 3' or 5' terminus of a polynucleotide molecules.
Expected Heterozygosity: Mean value of all the expected values found for all loci in a sample.
Expert System: A software program or set of software programs designed to rapidly process data without human intervention.
External testing: An external test is one that is created and administered by an outside agency.
First responder: The initial responding law enforcement officer and/or other public safety official or service provider arriving at the scene prior to the arrival of the investigators in charge.
Focal plane: A plane that is perpendicular to the axis of a lens or mirror and passes through the focus.
Forensic Hit: A CODIS match between two or more crime scene profiles.
Forensic Index: DNA profiles developed from crime scene evidence and uploaded into CODIS are maintained in the forensic index of the database.
Forensic Science: The application of science to analyze evidence involved in criminal and civil litigation.
Forensic unknowns: DNA profiles obtained from crime scene evidence samples that are unmatched to a known individual.
Fractions: The result of the differential extraction; separating sperm cells from all other DNA material.
Fragile evidence: Evidence that will lose its evidentiary value if not preserved and protected, either because of its nature or the conditions at the scene (e.g., blood in the rain).
Fusiform: Spindle-shaped; tapering from the middle towards each end. This shape is commonly seen in cortical cells and cortical fusi.
Gene: The basic unit of heredity; a functional sequence of DNA in a chromosome.
Genetic loci
Genetics: The study of the patterns of inheritance of specific traits.
Genome: All the genetic material in the chromosomes of a particular organism; its size is generally given as its total number of base pairs.
Genotype: The genetic constitution of an organism, as distinguished from its physical appearance (its phenotype). The designation of two alleles at a particular locus is a genotype.
Hair: One of the numerous fine and generally cylindrical filaments that grow from the skin or integument of animals, esp. of most mammals, of which they form the characteristic coat; applied also to similar-looking filamentous outgrowths from the body of insects and other invertebrates. These are usually of different structures.
Hair cuticular cast: A freely movable, firm yellowish-white material ensheathing scalp hairs resulting from scalp disorders such as psoriasis or seborrhoeic dermatitis.
Haplotype: A way of denoting the collective genotype of a number of closely linked loci on a chromosome.
Haptoglobin: A protein present in blood serum that combines with hemoglobin to form a complex that is rapidly removed from the circulation by the liver.
Hardy-Weinberg (Equilibrium): In a large random intrabreeding population, not subjected to excessive selection or mutation, the gene and genotype frequencies will remain constant overt time. The sum of p²+2pq+q² applies at equilibrium for a single allele pair where p is the frequency of the allele A, q is the frequency of a, p² is the frequency of genotype AA, q² is the frequency of aa, and 2pq is the frequency of Aa.
Heme: The deep red, non-protein, ferrous component of hemoglobin. C₃₄H₃₂FeN₄O₄
Heredity: The transmission of characteristics from one generation to the next.
Heteroplasmy: The presence of more than one mtDNA type within a single individual.
Heterozygosity: The probability that a given loci will be heterozygous in a randomly selected individual; having two different alleles at one locus.
Heterozygous: If two alleles are different at one locus, the person is heterozygous at that genetic location.
HIPAA: Health Insurance Portability and Accountability Act of 1996.
Histone: A type of basic protein that forms the unit around which DNA is coiled in the nucleosomes of eukaryotic chromosomes. Arginine- and lysine-rich basic proteins making up a substantial portion of eukaryotic nucleoprotein.
HLA DQ-alpha: A polymorphic gene in the Human Leukocyte Antigen (HLA) region of chromosome 6 that has been well studied and analyzed for many purposes including paternity testing, transplantation biology, and human DNA identification testing.
Homozygous: If two alleles at a locus that are indistinguishable, the person is homozygous at that genetic location.
Humic: An organic residue of decaying organic matter.
Hydroxyquinoline
Hypervariable: An area on the DNA which can have many different alleles in differing sequences.
Hypervariable Control Region: The D-loop of mitochondrial DNA in which base pairs of nucleotides repeat.
Immunoglobulin: A general term for the kind of globular blood proteins that constitute antibodies. A tetrameric protein composed of two identical light chains and two identical heavy chains. Specific proteins produced by derivatives of B lymphocytes that interact with and help protect an organism from specific antigens.
Included: Two samples could have come from the same source.
Inclusion (Failure to Exclude): The inability to exclude an individual as a possible source of a biological sample. This occurs when all types from a specific location in the DNA of a known individual are also present in the types for that specific location in the DNA obtained from an evidence sample.
Inconclusive: A situation in which no conclusion can be reached regarding testing done due to one of many possible reasons (e.g., no results obtained, uninterpretable results obtained, no exemplar/standard available for testing).
Indigo dye: A blue-colored dye that is derived from several plant species and commonly used to dye denim for blue jeans. A known PCR inhibitor.
Individualization: In forensic science, the process of attempting to associate an item of evidence with one and only one source.
Inhibitors: A substance that interferes with or prevents the polymerase chain reaction.; The border between the cuticle and the cortex.
Intercalating dye: A chemical that can insert itself between the stacked bases at the center of the DNA double helix, possibly causing a frameshift mutation.
Internal Size Standard (ISS): Specific DNA fragments of known sizes which are defined and used to size unknown fragments.
Internal testing: An internal test
Intimate Sample: An intimate sample is generally referred to a biological sample obtained from a source other than the mouth (saliva) and head (hair).
Irresolvable mixture: A DNA profile where multiple individuals have contributed biological material and no profile is more or less apparent than any other and the developed alleles cannot be isolated to a single source.
Isoamyl Alcohol: A chemical used in organic extractions to reduce the foaming of reagents, making it easier to detect the interface between the organic and aqueous phases.
Isoenzyme: Multiple forms of enzymes arising from genetically determined differences in primary structure. The term does not apply to those derived by modification of the same primary sequence.
John Doe Warrant: A warrant used when crime scene evidence yields a DNA profile but the individual corresponding to the DNA profile is unknown. In lieu of the suspect's name, the warrant will be filed as "John Doe" and cite the DNA profile.
Junk DNA: Stretches of DNA that do not code for genes; "most of the genome consists of junk DNA."
Keratin: Any of the various sulphur-containing fibrous proteins that form chemical basis for keratinized epidermal tissues such as hair, nails, feathers, and horns of animals.
Kinked: Hair that is closely curled or twisted.
Known samples: A DNA sample for which the source is known. These samples are generally obtained from the victim and/or suspected perpetrator of a crime, as well as from other persons whose DNA might be reflected when samples of the evidence are analyzed (could include a boyfriend, husband, or other third-party). These samples are also referred to as reference samples, since they serve as a reference to which the unknown DNA samples are compared with the goal of identifying the source of the unknown DNA samples.
Lanugo: The fine hairs found on the human fetus.
Latent print: A print impression that is not readily visible, made by contact with a surface.
LDIS: The Local DNA Index System of CODIS, which uploads forensic and offender DNA profiles to the State DNA Index System, or SDIS.
Length heteroplasmy: The presence of mtDNA molecules that differ in length.
Likelihood ratio: The ratio of two probabilities of the same event under different hypotheses. In DNA testing often expressed as the ratio between the likelihood that a given profile came from a particular individual and the likelihood that it came from a random unrelated person. Note that in this case the likelihood of each event does not add to give 1 (100% likelihood) as it does not incorporate the possibility of error or that the profiles came from twins or other near relatives.
Linkage Equilibrium
Lipopolysaccharides: A large molecule containing a lipid and a carbohydrate.; States that every time someone enters an environment, something is added to and removed from it. The principle is sometimes stated as "every contact leaves a trace," and applies to contact between individuals as well as between individuals and a physical environment. Local (LDIS); The Local DNA Index System of CODIS which uploads forensic and offender DNA profiles to the State DNA Index System, or SDIS.
Locus (pl. loci): The specific physical location of a gene on a chromosome.
Looped Cuticle
Low copy number: Refers to examination of less than 100pg (picograms) of input DNA.
Macroscopic: A term that describes characteristics large enough to be perceived without magnification; in forensic hair examination, this typically applies to unmounted hairs.
Magnification: The height of the image divided by the height of the object. The apparent enlargement of an object by an optical instrument.
Major contributor profile: A DNA profile where multiple individuals have contributed biologic material and one individual's DNA profile is more apparent.
Marker: Pieces of DNA sequence of known locations on chromosomes that are used to identify the specific genetic variations an individual possesses.
Match: Genetic profiles are said to "match" when they have the same allele designations at every loci.
Mean: The mean of sample is calculated by taking the sum of all data values and dividing by the total number of data values.
Measurement scale: An object showing standard units of length (e.g., ruler) used in photographic documentation of an item of evidence.
Medial: Towards the long axis of the hair.
Medulla: A series of air- or fluid-filled cells along the central axis of the hair.
Medullary Continuity: The continuous or discontinuous nature of the medulla.
Melanin: The pigment occurring in plants, animals, and protista. It is responsible for skin and hair pigmentation. Two forms of melanin, eumelanin and phaeomelanin, determine the color of human hair.
Melting Temperature T_m: The temperature at which one-half of a particular DNA duplex will dissociate and become single strand DNA.
Microbial Epidemiology: microbial: relating to a microbe or microbes; epidemiology: the study or the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems.
Microscope: An instrument consisting essentially of a tube 160 mm long, with an objective lens at the distant end and an eyepiece at the near end. The objective forms a real aerial image of the object in the focal plane of the eyepiece where it is observed by the eye.
Microscopic: A term for objects which are too small to be resolved by the unaided eye.
Midshaft Region: The region of the hair between the proximal and distal ends.
Minisatellite Variant Repeat (MVR): The temperature at which one-half of a particular DNA duplex will dissociate and become single strand DNA.
Mitochondrial DNA (mtDNA): The DNA found in the many mitochondria found in each cell of a body. The sequencing of mitochondrial DNA can link individuals descended from a common female ancestor.
Mongoloid: An archaic anthropological term designating peoples originating from Asia, excluding the Indian subcontinent but including the Native Americans.
Monilethrix: Monilethrix is a hair disorder that results in periodic nodes or beading along the length of the hair with intervening, tapering constrictions that are not medullated.
Morphology: Shape, form, external structure, or arrangement, especially as an object of study or classification
mtDNA types: A mtDNA type is the sequence of a region of mtDNA. Common sources of mtDNA are hairs, skeletal remains, and teeth.
Multiplexed: A system for analyzing several loci at once.
Mutation: Damaged or changed DNA anywhere along the DNA strand.
National DNA Index System (NDIS): Authorized by the DNA Identification Act of 1994, the FBI administers this national index. NDIS compares DNA profiles associated with a crime scene to DNA profiles collected from known convicted offenders, as well as to other crime scene profiles. When the DNA profiles are uploaded to NDIS, they are searched against the other DNA profiles submitted by other participating states.
National Research Council (NRC): The National Research Council was convened in 1989. In 1996 the NRC filed the report The Evaluation of Forensic DNA Evidence (referred to as NRC II). This document revised and expanded the initial report written in 1992 (NRC I). These recommendations are recognized by U.S. courts.
Negroid: An archaic anthropological term designating most of the peoples originating from Africa.
No results: A situation in which no interpretable results are obtained from testing a DNA sample. A finding of no results can be due to the absence of DNA, insufficient DNA, or substances that inhibit the PCR process, among others.
Non-conformances: Inconsistencies in laboratory practices that do not meet accreditation standards.
Nonmatch: An individual is eliminated as the source of a biological sample. This occurs when one or more types from a specific location in the DNA of a known individual are not present in the type(s) for that specific location in the DNA obtained from an evidence sample.
Nonporous Container: Packaging through which liquids or vapors cannot pass (e.g., glass jars or metal cans).
Nuclear DNA: The DNA found in the nucleus of a cell.
Nucleases: One of the several classes of enzymes that degrade nucleic acid. An enzyme that can degrade DNA or RNA by breaking phosphodiester bonds.
Nucleated: A nucleus or occurring in the nucleus.
Nucleus: The cellular organelle that contains most of the genetic material.
Numerical aperture: A measure of the information-collecting ability of a microscope optic. The greater the NA, the better the resolving ability. It is a measure of the light-gathering capacity of the lens system and determines its resolving power and depth of field.
Objective test: A test which having been documented and validated is under control so that it can be demonstrated that all appropriately trained staff will obtain the same results within defined limits. These defined limits relate to expressions of degrees of probability as well as numerical values.
Off Ladder (OL) Alleles: Alleles that size outside allele categories represented in the ladder.
Offender Hit: A CODIS match between a crime scene profile and an offender profile.
Offender Index: DNA profiles developed from qualifying offenders and uploaded into CODIS are maintained in the offender index of the database.
Ohm's Law: The amount of current flowing in a circuit made up of pure resistances is directly proportional to the electromotive forces impressed on the circuit and inversely proportional to the total resistance of the circuit.
Oligonucleotides: A molecule usually composed of 25 or fewer nucleotides; used as a DNA synthesis primer.
Optical Density (OD): Synonymous with absorbance. Absorbance is the logarithm of the ratio of incident to transmitted radiant power through a sample.
Outer Cuticle Margin: The border of the outermost edge of the cuticle.
Ovoid Bodies: Oval-shaped heavily pigmented bodies that may occur in the hair cortex.
Partial profile: DNA evidence that does not yield identifiable results in all 13 core loci.
Partially degraded DNA: Forensic DNA evidence exposed to environmental conditions that may prevent it from yielding a usable profile.
Paternal inheritance
Paternity or System Index (PI or SI): A statistic that compares the likelihood that a genetic marker (allele) that the alleged father passed to the child to the probability that a randomly selected unrelated man of similar ethnic background could pass the allele to the child.
PCR Inhibitors: A substance that interferes with the Polymerase Chain Reaction (PCR) process. Examples of PCR inhibitors include dyes, soil, chemicals, and heme (hemoglobin).
Peripheral Region: The peripheral region is the portion of the hair toward the outermost areas of the hair, including the cuticle and the outer areas of the cortex, distant from the medullary or central region.
Personal Protective Equipment (PPE): Articles such as disposable (latex) gloves, masks, shoe covers, and eye protection that are utilized to provide a barrier to keep biological or chemical hazards from contacting the skin, eyes, and mucous membranes and to avoid contamination of the crime scene.
Phenol: A chemical used in organic extraction. Polysaccharides and proteins are soluble in phenol, allowing for their separation from DNA. C₆H₅OH. See figure to the right.
Phenotype: The detectable outward manifestations of a specific genotype; the physical characteristics of a living object.
Pigmentation: Coloration or discoloration by formation or deposition of pigment in the tissues. In a forensic hair examination, the description of the aggregation, distribution, and density of pigment granules.
Pili Annulati: Pili annulati is a hair disorder that results in ringed or banded hair, alternating bright and dark bands in the hair shaft. The dark bands are a manifestation of the abnormal air spaces in the cortex.
Pili Bifurcati: A genetic hair disorder characterized by two hairs joined at the shaft along their entire length.
Pili Torti: A genetic hair disorder characterized by the hair shaft being flattened and twisted 180 degrees numerous times along its axis. It is usually found at irregular intervals along the shaft.
Polymerase Chain Reaction (PCR): A process used in DNA identification testing in which one or more specific small regions of the DNA are copied using a DNA polymerase enzyme so that a sufficient amount of DNA is generated for analysis.
Polymorphic: Variable, more than one kind.
Polymorphism: Variations in DNA sequences in a population that are detected in human DNA identification testing.
Polypurine: A stretch of adenine and/or guanine.
Polypyrimidine: A stretch of cytosine and/or thyamine.; FBI CODIS software program used to perform statistical DNA match estimates.
Population Genetics: The study of the distribution of genes in populations and of how the frequencies of genes and genotypes are maintained or changed.
Postmortem Root Banding: An opaque ellipsoidal band, composed of parallel elongated air spaces, which appear on the proximal portion of hair shafts from postmortem hairs, likely to be in the anagen growth phase.
Preferential Amplification: Imbalanced amplification or lack of amplification at a locus.
Presumptive Test: A screening test used to indicate the possible presence of the named body fluid.
Primer: A segment of DNA or RNA that is complementary to a given DNA sequence and that is needed to initiate replication by DNA polymerase.
Primer dimer: Formed by intermolecular interactions between the two primers (i.e., self-dimers and cross-dimers).