his glossary highlights some of the technological terms victim service providers may encounter when dealing with victims during a criminal investigation. Many terms have been used in this bulletin, but others are listed to give providers a more thorough understanding of the importance of DNA.

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 an A, B, O, or AB blood type by testing liquid or stains from body fluids (such as blood, saliva, vaginal secretions). One out of every three randomly selected pairs of people have the same ABO blood type.

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 of a biological sample.

Biological Evidence: Evidence commonly recovered from crime scenes in the form of hair, tissue, bones, teeth, blood, or other bodily fluids.

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 should include the name or initials of the individual collecting the evidence, each person or entity subsequently having custody of it, the dates the items were collected or transferred, where the items were collected, the agency and case number, the victim's or suspect's name (if known), and a brief description of the item.

CODIS: The Combined DNA Index System is an electronic database 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.

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

Degradation: The breaking down of DNA into smaller fragments by chemical or physical processes. Degradation of DNA may limit its use as evidence.

DNA: Deoxyribonucleic acid, often referred to as the "blueprint of life," is an organic substance found in nearly all cells. DNA determines each person's individual characteristics. An individual's DNA is unique except in identical twins. DNA in the cell nucleus is the genetic material inherited from our biological parents. The shape of DNA resembles a rope ladder that has been twisted (double helix).

DNA Advisory Board (DAB): Created under the DNA Identification Act of 1994, DAB established standards for forensic DNA testing laboratories and held its last meeting in fall 2000.

DNA Marker: A piece of DNA from a known location in the DNA molecule, which differs between people. The DNA marker is used to identify the specific genetic variations an individual possesses.

DNA Profile: A set of genetic characteristics that results from forensic DNA analysis of several DNA markers.

DNA Typing or Profiling: The process of testing to identify DNA patterns or types. In the forensic setting, this testing is used to indicate parentage or to exclude or include individuals as possible sources of body fluid stains (blood, saliva, or semen) and other biological evidence (bones, teeth, or hair).

Elimination or Reference Sample: A term used to describe a sample of known source taken for comparison purposes. An elimination sample is one of known source taken from a person who had lawful access to the crime scene to be used for comparison with evidence of the same type. Examples of elimination samples include blood or cheek (buccal) swabs for DNA analysis, fingerprints from occupants, tire tread impressions from police vehicles, or footwear impressions from emergency medical personnel. A reference sample is material of a verifiable/ documented source which shows an association or link between an offender, crime scene, and/or victim when compared with evidence of an unknown source. For example, a carpet cutting taken from a location suspected as the point of transfer for comparison with the fibers recovered from a 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.

Exclusion: A DNA test result indicating that an individual is excluded as the source of DNA evidence. In the context of a criminal case, exclusion does not necessarily mean a suspect is innocent.

Exemplar: A biological sample (such as blood or saliva) collected from a known individual to be used for comparison to DNA test results from evidence samples. Also referred to as a standard.

Inclusion: A DNA test result indicating that an individual is not excluded as the source of DNA evidence. In the context of a criminal case, inclusion does not necessarily mean a suspect is guilty.

Inconclusive Results: A situation in which no conclusion can be reached regarding testing done due to one of many possible reasons (such as no results obtained, uninterpretable results obtained, no exemplar/standard available for testing). Locus (pl. loci): The specific physical location of a gene on a chromosome.

Mitochondrial DNA: DNA found in the mitochondria in each cell of a body. The sequencing of mitochondrial DNA can link individuals descended from a common female ancestor.

Nuclear DNA: DNA found in the nucleus of a cell. DNA testing using RFLP, DQA1 (DQa), PM, D1S80, or STRs screen markers in nuclear DNA.

PCR: Polymerase chain reaction is 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. This process enables scientists to obtain genetic information from small or degraded specimens.

Polymorphism: Variations in DNA sequences in a population that are detected in human DNA identification testing.

Reference Sample: See Elimination or Reference Sample listing.

RFLP: Restriction fragment length polymorphism is a process used in DNA identification testing in which size (fragment length) differences at specific regions of the DNA are detected.

STR: Short tandem repeat(s) are small regions of the DNA that contain short segments (usually 2, 3, 4, or 5 bases long) repeated several times in tandem (side-by-side). Thirteen STR sequences have been selected as the genetic markers to be used in CODIS.

Substrates: Any background material upon which a biological sample has been deposited (e.g., clothing, glass, wood, or upholstery).

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Understanding DNA Evidence: A Guide for Victim Service Providers
April 2001