DNA so dangerous that it doesn’t exist in nature has been given its first useful role – keeping innocent people out of jail.

Several sequences of DNA not found in nature – probably because they are incompatible with life – were identified in 2007. Now it seems these so-called nullomers can be used to tag DNA samples taken from police suspects. If a suspect’s DNA was tagged and then accidentally mixed with a crime-scene sample it would place them at the scene when perhaps they were not. But the tag’s presence would prove that particular DNA sample came from sloppy lab or forensic practice and not the suspect.

Greg Hampikian of Boise State University in Idaho and his colleagues impregnated filter paper with various nullomers. The cards were then used to soak up and store DNA samples from a knife blade and a coffee cup lid.

Sure enough, even when Hampikian diluted the DNA samples 100,000 times, the nullomers were still identifiable, and didn’t interfere with analysis of the original DNA profile (Journal of Forensic and Legal Medicine, doi.org/mcf).

This article appeared in print under the headline “Killer DNA protects the innocent”