DNA - Terminology

Allele

The characteristics of a single copy of a specific gene, or of a single copy of a specific location on a chromosome.

Autosomal DNA

DNA found in chromosomes which are not sex chromosomes.

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

Combined DNA Index System (CODIS)

The generic term used to describe the FBI’s program of support for criminal justice DNA databases as well as the software used to run National DNA Index System (NDIS) databases; CODIS is made up of the National DNA Index System (NDIS), the State DNA Index System (SDIS) and Local DNA Index Systems (LDIS).

DNA (Deoxyribonucleic acid)

Often referred to as the “blueprint of life;” genetic material present in the nucleus of cells which is inherited from each biological parent that determines each person’s individual characteristics. An individual’s DNA is unique except in cases of identical twins.

DNA Profiling

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.

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, except identical twins; this technique became known to the public as “DNA fingerprinting” because of its powerful ability to discriminate between unrelated individuals.

Epithelial cells

Cells that cover the inner and outer linings of body cavities.

Forensic DNA Analysis

The process of identifying and evaluating biological evidence in criminal matters using DNA technologies.

Gene

a distinct sequence of nucleotides forming part of a chromosome, the order of which determines the order of monomers in a polypeptide or nucleic acid molecule which a cell (or virus) may synthesize

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.

Locus

The specific physical location of a gene on a chromosome; the plural form is loci.

Low Copy Number Analysis

The analysis of samples containing a small amount of DNA (approximately 30 cells or less); analysis of samples falling into this category often requires enhanced analysis methods to increase the sensitivity of detection.

Mitochondrial DNA (mtDNA)

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

National DNA Index System (NDIS)

Authorized by the DNA Identification Act of 1994, the FBI administers this national index. NDIS enables comparison of DNA profiles associated with a crime scene to DNA profiles collected from known convicted offenders, as well as to other crime scene profiles. DNA profiles uploaded to NDIS are searched against the other DNA profiles submitted by other participating states.

Nuclear DNA

DNA located in the nucleus of a cell.

Partial DNA Profile

DNA evidence that does not yield identifiable results in all 13 core loci.

Quality Assurance Standards (QAS)

Quality assurance methods developed by the Scientific Working Group of DNA Analysis and Methods (SWGDAM). QAS provides guidelines to ensure the quality and integrity of data generated by the laboratory and uploaded into the CODIS database(s); published by the FBI.

Reference Samples

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.

Short tandem repeat (STR)

Multiple copies of a short identical DNA sequence arranged in direct succession in particular regions of chromosomes

Y-STR

STR located on the Y chromosome; often examined when investigating sexual assaults involving male suspects.

X chromosome

Females

Y Chromosome

Males