Evil twins are so common in the media, we're surprised that mothers don't automatically kill one of their two infants to prevent the evil from spreading. But in reality, twins commit crimes as infrequently as the rest of the us. And now, like the rest of us, they can be identified by their DNA.
After genetic material (such as blood and semen) is collected from a crime scene, technicians isolate the DNA and copy it using PCR (polymerase chain reaction). They then study the subject's STR markers and compare it to the known suspect and/or population database. If the DNA matches a known person, we have a winner (who is also a loser) ... except in the case of identical twins.
In the few cases in which a twin (or worse, both twins) is suspected of a crime, investigators can only determine whodunit by sequencing their entire genome. However, it's an expensive procedure.
According to New Scientist, Graham Williams at the University of Huddersfield, UK, reasoned that although the twins may have the same genetic material, they also have unique experiences and lifestyles. Enter epigenetics.
New Scientist writes, "[E]pigenetic changes occur when a chemical group known as a methyl group attaches to a gene and modifies the way it is expressed. This happens as a body is influenced by a person's environment, lifestyle and disease."
In other words, Orphan Black's former hard-partier Sarah would have a different methyl group than binge-eating, binge-killing Helena.
With that in mind, Williams' team extracted DNA from five pairs of twins and "used a chemical to target parts of the DNA that did not have methyl groups attached, and change the number of hydrogen bonds at these points. Any difference in the number of hydrogen bonds should change the melting point of a compound."
The two different samples now melt at different temperatures. Voila, instant identification.
Beware, evildoing twins. Your days of hiding behind your DNA are officially over.