Identical twins share an identical DNA profile, and when you're an investigator examining DNA evidence, that can be a problem. The cases may be rare, but they exist, legal expert Jennifer Mnookin told the New York Times last year amid a rape case involving a suspect with a twin: "There certainly have been instances where identical twins have laid blame on the other, or each denied responsibility, and for a lack of persuasive evidence they’ve both gotten off." But new research could help prosecutors get past that hurdle, Science Daily reports. British scientists have found that by heating DNA to its "melting temperature," they can distinguish between twins. In what the researchers call "high resolution melt curve analysis," heat is applied to DNA; the melting temperature refers to the temperature at which the hydrogen bonds in our DNA break.
Environmental factors can alter the number of hydrogen bonds in a DNA sequence: One twin could be a smoker, for instance, or be exposed to more sunlight. More bonds lead to a higher melting temperature. To arrive at their findings, published in Analytical Biochemistry, researchers had five sets of identical twins supply their DNA via a cheek swab; using HRMA and looking at two genetic markers, the researchers were able to distinguish between all five sets in one case, and four of the five in the case of the second marker. But some issues remain, lead researcher Dr. Graham Williams notes. One is that the process requires "a high sample quantity" of DNA that might not be available at a crime scene. (This week, a man's charges were dropped—in part thanks to DNA evidence—after he had spent 36 years in prison.)