Glossary

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.

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.

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.

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.

Amplification - Producing multiple copies of a chosen DNA region, usually by PCR (Polymerase Chain Reaction).

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

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.

Bench notes - A laboratory analyst's recorded notes.

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.

Boundaries - The perimeter or border surrounding potential physical evidence related to the crime.

Cambridge Reference Sequence (CRS) - A "master template" of the HVR-1 region of mitochondrial DNA.

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

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.

Cell - The smallest component of life capable of independent reproduction and from which DNA is isolated for forensic analysis.

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.)

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.

Competency - The combination of demonstrated knowledge, skills, and abilities.

Contamination - The undesirable transfer of material to physical evidence (DNA) from another source.

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.

Cross Contamination - The undesirable transfer of material between two or more sources of physical evidence.

Cytoplasm - The viscid, semifluid matter contained within the plasma membrane of a cell, excluding the nucleus.

Degradation - The fragmenting, or breakdown, of DNA by chemical or physical means.

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.

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).

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).

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.

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 an association or linkage 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).

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.

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.

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).

Gene - The basic unit of heredity; a functional sequence of DNA in a chromosome.

Genetic loci - Places in the genetic material of an organism where specific DNA sequences can be found.

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.

Haplotype - A way of denoting the collective genotype of a number of closely linked loci on a chromosome.

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.

Heredity - The transmission of characteristics from one generation to the next.

Heteroplasmy - The presence of more than one mtDNA type within a single individual.

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.

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.

Hypervariable - An area on the DNA which can have many different alleles in differing sequences.

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).

Internal testing - An internal test is one that is created and administered by the laboratory itself.

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.

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."

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.

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 - When two or more genetic loci appear to segregate randomly in a given population. The genotypes appear randomly with respect to each other.

Locus (pl. loci) - The specific physical location of a gene on a chromosome.

Low copy number - Refers to examination of less than 100pg (picograms) of input DNA.

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.

Measurement scale - An object showing standard units of length (e.g., ruler) used in photographic documentation of an item of evidence.

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.   

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.

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.

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.

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.

Nucleated - A nucleus or occurring in the nucleus.

Nucleus - The cellular organelle that contains most of the genetic material.

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.

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.

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 - Genetic material which is inherited from one’s father; for example, the possibility that mtDNA can be inherited from one’s father.

PCR Inhibitors - A substance that interferes with the Polymerase Chain Reaction (PCR) process. Examples of PCR inhibitors include dyes, soil, chemicals, and heme (hemoglobin).

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.

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.

PopStats - FBI CODIS software program used to perform statistical DNA match estimates.

Probability - The chance of observing a particular future event; a simple ratio of the number of observed events divided by the total number of possible events.

Probability calculations - Predictions based on small sampling of a larger population.

Probability of Exclusion - The probability that a random individual would be excluded as the source of analyzed DNA evidence.

Probability of inclusion - The probability that a random individual would be included as a potential source of analyzed DNA evidence.

Product rule - The product rule calculates the expected chance of finding a given STR (short tandem repeat) profile within a population by multiplying the frequency of occurrence of the combination of alleles (genotype) found at a single locus, by the frequency of occurrence of the genotype found at the second locus, by the frequency of occurrence, in turn, of each of the other genotypes at the remaining STR loci.

Proficiency testing - A DNA proficiency test uses biological samples to assess a lab analyst's ongoing competency and the laboratory's ability to produce accurate results.

Pull-up - Specifically related to ABI Gene Scan® software, a peak seen in one color that is not due to the presence of DNA, but to incorrect compensation for the spectral overlap of the four dyes used in detecting multiple loci in one reaction. See also: Artifact

Quality Assurance (QA) - A program conducted by a laboratory to ensure accuracy and reliability of tests performed.

Quality Assurance Standards - The standards originated from the DNA Advisory Board and are maintained by the FBI; they place specific requirements on labs involved in forensic DNA analysis, both casework and convicted offender databasing.

Random match probability - The probability that the DNA in a random sample from the population has the same profile as the DNA in the evidence sample.

Reciprocal Discovery - Some jurisdictions enable a prosecutor by motion to request that the defense provide specific discovery material to the prosecution.

Recombination - The reversal of coupling phase I meiosis as gauged by the resulting phenotype. See also Recombinant DNA above.

Reference Samples - A standard/reference sample is material of a verifiable/documented source which, when compared with evidence of an unknown source, shows an association or linkage 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 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).

Restriction enzyme - A protein harnessed from bacteria that recognizes specific, short nucleotide sequences and cuts DNA at those sites.

Restriction fragment length polymorphism - Variation in the length of a stretch of DNA; abbreviated RFLP.

SDIS - State DNA Index System containing the state-level DNA records uploaded from local laboratory sites within the state. SDIS is the state's repository of DNA identification records and is under the control of state authorities. The SDIS laboratory serves as the central point of contact for access to the National DNA Index System (NDIS). The DNA Analysis Unit I (DNAUI) serves as the SDIS laboratory for the FBI.

Sequence (or site) heteroplasmy - Presence of mtDNA molecules that have different nucleotides at the same address.

Sequencing - Determination of the order of base sequences in a DNA molecule.

Short Tandem Repeats (STR) - Multiple copies of a short identical DNA sequence arranged in direct succession in particular regions of chromosomes.

Single Nucleotide Polymorphisms (SNPs) - DNA sequence variations that occur at a single nucleotide (A,T,C,or G).

Single source profile - A DNA profile where only one individual has contributed biologic material.

Single-use Equipment - 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).

Standard Operation Procedures (SOP) - A prescribed procedure to be followed routinely.

Stochastic effects - Being or having a random variable.

Short Tandem Repeat (STR) typing - DNA analysis method which targets regions on the chromosome which contain multiple copies of an identical DNA sequence in succession.

Stutter - A minor band or peak appearing one repeat unit smaller than a primary STR (short tandem repeat) allele. Occasionally, the repeat unit is larger than the primary allele.

Substrate - Any background material upon which biological sample has been deposited (e.g., clothing, glass, wood, upholstery).

SWGDAM - Scientific Working Group of DNA Analysis and Methods, formerly called TWGDAM (Technical Working Group on DNA Analysis and Methods).

Third Party Defense Motion - A motion filed by the prosecution to preclude the defense from asserting that DNA evidence is derived from a third party, possibly a relative of the accused.

Threshold value - A relative fluorescent unit (RFU) value that must be exceeded to make an allele call. This value will vary among laboratories.

Trace evidence - Physical evidence that results from the transfer of small quantities of materials (e.g., hair, textile fibers, paint chips, glass fragments, gunshot residue particles).

Uninterpretable - Results which might be reported by the laboratory when alleles can not be interpreted.

Upper Bound Frequency Estimates - an estimate of the percentage of individuals who could be potential contributors of a mtDNA profile.

UV light source - Use of an ultraviolet light source to enhance or visualize potential 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.

Validation - The process of extensive and rigorous evaluation of DNA methods before acceptance for routine use.

Variable Number of Tandem Repeats (VNTRs) - Repeating units of a DNA sequence; a class of RFLPs (restriction fragment length polymorphism); abbreviated VNTR.

Variant - A dissimilarity in the commonly occuring sequence of a gene.

Walk-through - An initial assessment conducted by carefully walking through the scene to evaluate the situation, identify potential evidence, and determine resources required. It can also be a final survey conducted to ensure the scene has been effectively and completely processed.

Y-STR - short tandem repeats located on the Y chromosome.