DNA Test That Distinguishes Identical Twins May Be Used in Court for First Time

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Normally, forensic tests work by extracting and amplifying regions of DNA collected from a crime scene. Then, investigators look for a match between the evidence and a suspect’s genetic sequence. Ordinarily, this kind of testing is sufficient: Most humans vary from one another enough for investigators to easily identify whether a suspect left blood, skin, hair, semen, or something else at a crime scene.

This is not true with identical twins. Grown from the same, single fertilized egg, monozygotic twins have nearly identical genomes. So, for decades, twins committing crimes had a relatively easy way to establish doubt—based on DNA evidence alone, their identical sibling would be equally as likely to have deposited whatever genetic material might have been left at a crime scene.

Maybe not anymore.

Using what’s known as ultra-deep, next-generation sequencing, a team in Germany has developed a test that claims to reliably identify which twin a biological sample belongs to. The test works by taking a close look at the genetic letters (called base pairs) comprising the 3 billion-base-pair human genome. Because mutations randomly occur during development, even genetically “identical” twins will vary at a handful of locations, says Burkhard Rolf, a forensic scientist at Eurofins Scientific, the company that developed the test.

The sequence mutations are random, so it’s incredibly unlikely they’d be the same in both twins—and it’s those discrepancies that can be used to pin a crime on a twin.

http://www.wired.com/2014/12/genetic-test-distinguishes-identical-twins-may-used-court-first-time/