Crime Scenes and Fingerprints...With a Trace

Enough DNA to perform DNA "fingerprinting" can be obtained from regular fingerprints - the kind that detectives (like CSI Investigators) typically hope are present at the scene of the crime; the kind the CSI Investigator means when asking a colleague, "Get any DNA??"

Forensic scientists, law enforcement officials, criminal lawyers and the courts have come increasingly to rely on DNA "fingerprints." The DNA for "fingerprinting" is usually obtained from blood, bone, hair, other body fluids, and tissues.

About 99.9% of our DNA is invariable. The composition of a person's DNA uniquely identifies that particular individual. The DNA is why humans are human.

Conversely, 0.1% (one-tenth percent) of the DNA differs from one person to the next. That may not seem like much of a difference. But this difference in DNA involves some 3 million chemicals called bases (3 million bits of variable genetic information). It is this variation that makes each of us (except identical twins) genetically unique. It also makes each of us uniquely identifiable!

Swabs taken from objects, such as door knobs or telephones that someone has touched, yield enough DNA for DNA "fingerprinting," according to a report by R A H van Oorschot and M K Jones published in the June 19, 1997 issue of the journal Nature (vol 387, page 767, 1997). In fact, a swab can yield enough DNA to tell if several individuals may have had their hands on the murder weapon (as in Agatha Christie's "Murder on the Orient Express").

The authors point out that the DNA swabbed from fingerprints provides a powerful forensic tool. Extreme caution is required, they warn, in handling evidence and interpreting DNA "fingerprints" made from fingerprints.

Last Editorial Review: 5/7/2003

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