Scientists may finally have cracked the code to using DNA to differentiate a specific individual from a set of identical twins.
Since it was first introduced to the courts in the 1980s, DNA analysis has transformed the way we approach criminal investigations.
But, despite more than 30 years of advancements since, there’s still one scenario that can stand in the way of nailing down the right suspect even when DNA is present: identical twins.
Identical twins arise from the same fertilized egg, and standard DNA tests are so-far unable to pinpoint the minute differences.
The identical twin problem has stood in the way of both criminal investigations and paternity tests, researchers explain in a new study published to the journal Plos One.
With their new test based on DNA sequencing, however, the team may finally have broken ground.
Instead of looking at hundreds or even thousands of mutated segments to spot the differences between twins, researchers behind the new study propose comparing their entire genomes.
The current techniques are ‘hampered by the fact that the two individuals usually coincides for the genetic markers tested,’ the researchers explain.
But thanks to recent advances in genome sequencing, it’s now possible to assess DNA in much greater detail than ever before.
Identical twins – or monozygotic (MZ) twins – may start out from the same egg, but each take on their own mutations as they develop.
It’s these mutations that could help to reveal who in a pair is tied to a given DNA sample.
Doing this accurately would require ‘a genome-wide search for those few mutations that occur during early embryonic development and hence allow distinguishing between MZ twins in later life,’ the researchers say.
Lead author Michael Krawczak has been investigating the possibility of comparing twins’ unique mutations for years, and published a set of initial calculations in 2012 to settle a hypothetical paternity dispute.
A team at Eurofins Scientific in Brussels then picked up on the research and tested it out themselves using DNA from a pair of identical twin volunteers, and the wife and child of one of the men, according to the New York Times.
Krawczak’s team has now published a general mathematical framework to back up the method, in a step toward its use in forensic investigations.
But, it’s still in the early stages and will require much more testing before it can be adopted by the courts, experts note.
Steven A. McCarroll, a Harvard Medical School geneticist who was not involved in the study, told NYT, ‘It would be really nice to know that we could do this kind of analysis over and over and over again and never get it wrong.’
Twins are two individuals who form in the same uterus. There are a few different kinds:
1. FRATERNAL TWINS (non-identical)
These account for two-thirds of twins.
Two eggs are fertilized by two sperm and both implanted into the walls of the uterus at the same time.
These eggs form separately, in separate sacs adjacent to each other.
They share 50 percent of their DNA, as they would with their other non-twin siblings.
They can be different genders, though most (around 60 percent) are same-sex twins.
Research suggests fraternal twins run in families, typically down the maternal line.
2. IDENTICAL TWINS
A single egg is fertilized by one sperm and embeds in the uterus wall.
But at some point, it splits from one zygote into two.
They do not always share the same amniotic sac, but they always share the same placenta.
Those that share the same amniotic sac are known as monoamniotic, while those that have their own are diamniotic.
Most identical twins split within eight days of conception.
Those that split between eight and 12 days are known as mono-mono twins – incredibly rare.
Those that split after 12 days tend to be conjoined.