Deoxyribonucleic acid (DNA) analysis can occur in body fluid stains and other biological tissues recovered from items of evidence. The DNA testing results obtained from evidence samples are compared to DNA from reference samples collected from known individuals. Such analyses may be able to associate victims and suspects with each other, with evidence items, or with a crime scene. The FBI can conduct nuclear, Y-chromosome, and/or mitochondrial DNA testing on evidence samples as appropriate.
The DCU performs serological testing to detect and characterize body fluids such as blood and semen on items of evidence.
Nuclear DNA (nDNA) is the most discriminating and is typically analyzed in evidence containing body fluids, skin cells, bones, and hairs that have tissue at their root ends. The power of nDNA testing lies in the ability to identify an individual as being the source of the DNA obtained from an evidence item, or by excluding an individual as a contributor to the DNA evidence.
Y-chromosome DNA testing is a form of nuclear DNA testing that is specific to the male chromosome, also known as the Y-chromosome. This type of testing can be useful for sexual assaults, missing persons, and intelligence cases. The Y-chromosome is transmitted from father to son as a complete set; therefore, anyone in the paternal lineage will have the same Y-chromosome profile. Due to multiple relatives having the same Y-chromosome profile, unique identifications are not possible from Y-chromosome analysis.
Mitochondrial DNA (mtDNA) is a form of DNA that is transmitted from mother to child in a complete set; therefore, anyone in the maternal lineage will have the same mtDNA profile. This type of DNA testing can be useful on evidence items such as naturally shed hairs, hair fragments, bones, and teeth. MtDNA analysis is highly sensitive and may allow scientists to obtain information from items of evidence associated with cold cases, missing persons, samples from mass disasters, and small pieces of evidence containing little biological material. However, since multiple individuals can have the same mtDNA profile, unique identifications are not possible from mtDNA analysis.
The DCU offers kinship analysis, which is the comparison performed to determine the possible familial relatedness between an evidence item and a known item using a software program. The DCU also offers criminal paternity testing as part of criminal, intelligence, and missing person casework. When appropriate, DNA results from evidence relating to criminal cases and missing persons will be uploaded into the National DNA Index System (NDIS).