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 diagnosis 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 some material: 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 a suspected individual is convicted of the crime, his or her DNA polymorphisms are put into a data bank system that is accessible by law enforcement officials. This system is referred to as CODIS or "Combined DNA Index System." This system has helped to solve many crimes and also to clear those wrongfully accused of a crime.
Other uses of identity testing are to identify individuals whose identity cannot be distinguished by other means, as with decomposed bodies. In this type of genetic testing, specific parts of DNA are examined for polymorphisms (differences) that are unique to the individual. These parts of the DNA strand are referred to as microsatellites or minisatellites and are composed of repeated subunits of the DNA strand. Sometimes these repeated units are called short tandem repeats (STRs) or variable number of tandem repeats (VNTRs). In forensics, these unique sequences are given the name "DNA fingerprint."
Other types of identity 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."
For more on this, see the World of Forensic Laboratory Testing: Genetic Tests and DNA Typing.