How Did DNA Change Forensics?


Deoxyribonucleic acid---DNA--is our unique genetic signature. Inherited over generations, it indelibly inscribes our singular existence in the cosmos. In grittier, down-to-earth applications, it has also forever changed forensics. Science can now leverage DNA's discrete genetic code to convict the guilty, free the innocent and put a name to even the tiniest traces of human remains.


  • That was not always the case. Before 1985, when British geneticist Alec Jeffreys discovered DNA's potential to make rock-solid identifications, it was often impossible to directly link a person to evidence obtained from crime scenes, resulting in thousands of unsolved crimes and untold numbers of wrongful acquittals and, worse, errant convictions. Blood evidence collected at a crime scene could, at best, only be said to match a suspect's blood, not that it belonged to the person. Fingerprints, when available, provided a stronger identification but were still open to interpretation and challenge. DNA immediately changed all that. In its first use in a criminal investigation, DNA fingerprinting cleared the chief suspect in two U.K. murders in 1987 and a year later helped convict the real killer.

Jeffreys' Discovery

  • Geneticist Jeffreys found that specific areas of DNA comprised stretches of repeated sequences, one after another, and that the quantity of the repeats he found was unique to different people. He went on to pioneer molecular genetics techniques to identify people through their DNA.

Collecting Evidence Containing DNA

  • Advances in molecular biology and diagnostic pathology have made it easier to analyze more accurately even microscopic (nanogram to picogram) quantities of DNA found in hair, skin, saliva or other tissue. Once the sample has been collected, it must be stored appropriately. Freezing at -80 degrees Celsius and protecting the sample from light, for example, will allow it to be stored for more than two decades. That ability to analyze biological evidence, perhaps decades after a crime, is unprecedented and has revolutionized criminal investigation.

DNA in Forensic Evidence

  • The wide-ranging variety of criminal cases that uses DNA forensics includes paternity tests, missing-persons investigations, natural disasters and mass victims and historical criminal investigations. It also includes identifying animal species being illegally traded by poachers, historical investigations, paternity testing, and verifying imports of wine and caviar.

Identification of 9/11 Victims

  • The 2001 attack on New York City's World Trade Center claimed almost 3,000 lives and produced 20,000 fragments of human remains. The medical examiner's office established a database of DNA profiles to serve an ongoing effort to identify as many victims as possible. DNA forensics have also been used to identify the Peruvian Ice Maiden and children who disappeared in Argentina in the 1970s and to verify the claims of people who insist they were related to the murdered last Czar of Russia, Nicholas Romanov.

DNA Profile Databases

  • Law enforcement officials can link DNA profiles to known crimes and criminal evidence through a computing tool known as CODIS, or the COmbined DNA Index System. Two main databases---one with DNA profiles of violent criminals and a second with DNA profiles derived from crime scenes---lets investigators rapidly match evidence in a crime with potential suspects. CODIS has become so efficient in identifying criminals, however, that a backlog of cases is now waiting to be prosecuted.


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