DNA fingerprinting is the analysis of genetic material to help identify people in civil and criminal cases. It is also called DNA typing or DNA analysis. The genetic material is deoxyribonucleic acid or DNA (see DNA ). It is found within the body’s cells. In forensic DNA analysis, investigators obtain and analyze DNA from the cells of people involved in legal investigations. The cells may come from almost any body fluids or tissues. Common sources include bone, teeth, blood, skin, semen, hair, and saliva. All humans, except for identical twins, have unique DNA that can be used to identify them.
Forensic DNA analysis is often used in criminal cases. Its use is based on the extreme unlikelihood that any two unrelated people would have identical DNA. Forensic investigators may compare DNA found at a crime scene with DNA collected from a suspect. The comparison may exclude or include the suspect as a possible source of the genetic material. In addition, law enforcement agencies have created large state, regional, and national DNA databases. These databases store genetic profiles of known criminals as well as those of unidentified individuals who left DNA at crime scenes. Such databases enable investigators to link known criminals to unsolved crimes. They also help to link separate crimes committed by the same unknown person.
DNA fingerprinting is also used in civil cases to settle questions of paternity, which involve determining the identity of a person’s father. In such cases, the use of DNA fingerprinting relies on the fact that half of a person’s DNA comes from the father.
Most DNA fingerprinting done today uses a technique called polymerase chain reaction (PCR). This technique involves the use of an enzyme to create many copies of a DNA sample. The copies can be used for comparison between samples.
The British geneticist Alec Jeffreys first proposed forensic DNA analysis in 1984. Jeffreys’s technique was first used in England in 1986 to prove the innocence of a person who had falsely confessed to murder. The first conviction based on DNA fingerprinting came in a rape trial in England in 1987. In the United States, DNA fingerprinting was first used as evidence in 1986 in Pennsylvania. Since then, it has become widely accepted by courts. Evidence from DNA fingerprinting has been used to exonerate (prove innocent) hundreds of people wrongly convicted of crimes.
