Identity testing is sometimes referred to as “DNA testing”, a term most frequently used in relation to criminal investigations. "DNA testing" is an unfortunate misnomer as all types of genetic analysis, whether for disease or identification or for tissue typing, involves assessment of DNA or RNA.
Identity testing focuses on the identification of an individual through the analysis of either nuclear or mitochondrial DNA extracted from blood, tissue, hair, bone, etc. Any material that contains cells with nuclei can be used for nuclear DNA extraction and eventual identity testing. Mitochondrial DNA, which is “extra-nuclear,” is used when a sample is severely degraded or if only hair shafts with no attached cells are available.
Increasingly, identity testing is used to identify a suspect in a criminal investigation by comparing the DNA found at a crime scene to that of the suspected individual. If the suspected individual is convicted of the crime, his or her DNA polymorphisms are put into a data bank that is accessible to the police force.
Other uses of identity testing include finding the identity of those who cannot be distinguished by other means, as with decomposed bodies. In this type of forensic genetic testing, patterns of polymorphism specific to an individual are used to produce a “DNA fingerprint.” DNA sequences that are particularly susceptible to polymorphic variation are useful for this purpose including DNA sequences known as microsatellites, minisatellites, short tandem repeats (STRs) and variable number tandem repeats (VNTRs).
Other applications of this type of testing include the determination of an individual’s parent or parents, often called “parentage testing”, and identifying organ donors by using genetic testing for tissue transplantation, called "tissue typing" (see below).