BBC It's well known that identical twins are not totally identical - they can, usually, be told apart, after all. But up to now it has been almost impossible to distinguish their DNA. It's claimed that a new test can do it quickly and affordably, however - and this could help police solve a number of crimes.
At the end of 2012, six women were raped in Marseille, in the south of France. Evidence, including DNA, led police to not one, but two suspects - identical twins Elwin and Yohan. Their surname was not revealed. When asked to identify the attacker, victims recognised the twins but couldn't say which one had assaulted them.
Police are struggling to work out which one to prosecute. They have been holding the brothers in custody since February - each twin says he didn't carry out the attacks, but neither is blaming the other.
When the twins were arrested, media reports said tests to determine who to charge with the crimes would be prohibitively expensive, but that looks set to change. Scientists specialising in genomic research at the Eurofins laboratory in Ebersberg, Germany, say they can now help in cases like this.
"The human genome consists of a three-billion-letter code," says Georg Gradl, their next-generation sequencing expert. "If the body is growing, or an embryo is developing, then all the three billion letters have to be copied.
"During this copying process in the body there are 'typos' happening," says Gradl, referring to slight mutations.
In standard DNA tests only a tiny fraction of the code is analysed - enough to differentiate between two average people, but not identical twins.
Gradl and his team took samples from a pair of male twins and looked at the entire three-billion-letter sequence, and they found a few dozen differences in their DNA.
The scientists also tested the son of one of the men, and found he had inherited five of the mutations from his father. Having analysed the results, they are confident that they can now tell any twin from another, and from their children.