A private lab in Dallas will try something never attempted by scientists who investigate crimes: separate the DNA of identical twins to show which member of the pair committed a crime, reports USA Today. Twins begin life with the same genetic profile because they are formed when a single fertilized egg divides. Tiny mutations are known to occur in DNA; The lab, Orchid Cellmark, hopes to identify those differences to distinguish between the DNA of twins from Grand Rapids, Mich. The DNA of both men matches a semen sample from a November 1999 rape that was committed by one man.
In several cases, genetic evidence left at crime scenes – typically blood or semen – has linked identical twins to crimes that only one could have committed. The DNA testing used by law enforcement authorities and the FBI’s national DNA database of convicted felons does not detect differences between identical twins. Police in Virginia, Massachusetts, and Texas have had a half-dozen such cases during the past two years.