Hard to tell apart, especially genetically (Image: John Lamb/Getty)

Whodunnit? Standard DNA analysis can pin down a guilty criminal, but it can be tough if the suspects are identical twins, who share the same genetic code.

Around the world there have been several cases in which police have been unable to prosecute a suspect because he or she is an identical twin.

But there is now a test involving melting DNA that could tell identical twins apart in a matter of hours and reveal who that genetic material came from.


To find out if a suspect’s DNA matches that recovered from the scene of a crime, forensic scientists compare parts of DNA sequences that are known to be especially variable between individuals. This isn’t useful when two identical twins are both suspects. In these cases, scientists can sequence the entire genome of both individuals and look for any subtle, rare differences that may have resulted from genetic mutations, but the procedure is expensive and takes about a month.

Quick ‘n’ easy

Graham Williams at the University of Huddersfield, UK, has a different way – to look for modifications to the twins’ DNA that have come about as a result of their lifestyles.

Such epigenetic 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.

Williams’s team took mouth swabs from five pairs of twins. After extracting the DNA from each sample, the group 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.

When the team heated up the twins’ DNA samples, they found the melting points were different – allowing them to tell the twins apart genetically. The test was also much quicker than whole genome sequencing, says Williams. “It can be done in just a few hours.”

It’s a step forward when it comes to quickly and cheaply pinning a DNA sample to a particular twin, says Georgina Meakin at University College London. But she says that twins who share the same environment and habits might not have many epigenetic differences.

Journal reference: Analytical Biochemistry, DOI: 10.1016/j.ab.2015.02.001