DNA (or deoxyribonucleic acid) is a nucleic acid which contains the genetic instructions used in the development and function of all life. The instructions and information contained in the genes are unique to the particular life form which they originate.

Because of this, DNA has become one of our most powerful forensic tools. This led to one of readers to ask, “Can DNA samples be faked?”

DNA Not So Bulletproof Anymore?

DNA for use in criminal forensics is widely accepted as nearly bulletproof, indisputable evidence. This confidence can be attributed to its error margin, which is so low; it excludes the rest of our planet’s population. The odds of an incorrect match are in the billions – higher than winning your state lottery.

Other forms of evidence, like blood-spatter analysis and ballistics, relies on expert judgment and is considered to have a more limited connection with established science. DNA evidence in forensics surpasses those methods and is considered to be more reliable than even eyewitness evidence, which can suffer from a relatively higher error rate.

Fake DNA Evidence

Things have changed recently, when in late 2009, scientists in Israel demonstrated the ability to fabricate DNA evidence. The researchers created saliva and blood samples containing DNA from another person other than the original donor. The researchers took blood from a woman and centrifuged it to remove the white cells, which contain DNA. They then added DNA to the remaining red blood cells, which had been amplified from a man’s hair follicle.

They also demonstrated the ability to manufacture a sample of DNA with only a DNA profile from a database – without obtaining any physical samples from that person. They did this by cloning tiny DNA snippets from the most common variants at each spot and creating a repository of snippets. To create the desired DNA sample, they simply mixed the proper snippets together. They claim that a repository of just 425 different DNA snippets would be enough to cover every possible human profile.

The researchers also mention a way of spotting DNA which has been fabricated – a lab would just have to look for a lack of methylation. Methyl groups are found naturally in genetic code, but they are not found in the ‘fake’ DNA.

An arms race between the forensic techniques and the sophistication of fabrication is unlikely as your average criminal is not going to have the equipment and skills needed to pull a fake off. However, the fact that it’s possible at all may very well undermine the long-lived general confidence in the use of DNA evidence in forensics. To keep the confidence forensics has enjoyed these last two decades, labs would have to begin looking for a lack of methylation and make it a standard practice.

References:

Scientific American “Lab creates fake DNA evidence” (2009)

“DNA Identification in Mass Fatality Incidents“. National Institute of Justice. (2006)

Alberts, Bruce; Keith Roberts and Peter Walters (2002). Molecular Biology of the Cell; Fourth Edition

Jeffreys A, Wilson V, Thein S (1985). “Individual-specific ‘fingerprints’ of human DNA“. Nature 316 (6023): 76–9. Bibcode 1985Natur.316…76J.