Crime Scene Genetics: Transforming Forensic Science through Molecular Technologies

摘要

Advances in DNA (deoxyribonucleic acid) technology over the past 25 years have led to spectacularly precise forensic identification techniques, although some applications have also unleashed controversies regarding genetic privacy. Current molecular forensic work is pushing these technologies even further by analyzing extremely damaged DNA and by introducing RNA (ribonucleic acid) techniques to forensics.nnIn 1986, a British teenager named Richard Buckland admitted under police questioning that he had raped and murdered 15-year-old Dawn Ashworth in Leicestershire, England. He denied, however, any connection to a three-year-old murder that police were convinced had been committed by the same person. Had this happened just a year or two earlier, Buckland may have gone to prison for one or both murders. But a new technique, called DNA fingerprinting, conclusively demonstrated that semen found at both crime scenes did not belong to Buckland.nnLeicestershire police and the United Kingdom's Forensic Science Service conducted a mass DNA screening of local men, looking for a match to the genetic profile of the murderer. They found nothing—until a man was overheard saying that he had given a DNA sample in place of his friend Colin Pitchfork. After Pitchfork was tracked down, he quickly became the first person convicted for murder on the basis of DNA evidence.nnUntil the 1980s, such precise identification of a suspect was unheard of. If someone left a drop of blood at a crime scene, forensic scientists could analyze only the person's blood type plus a few proteins that exist in slightly different versions in different people. But neither of these tests is particularly specific: many people share blood types and protein markers, making unique identification from a blood stain nearly impossible.nnThe course of molecular forensics changed in 1984, when geneticist Alec Jeffreys, of the University of Leicester in the United Kingdom, discovered a new type of marker in the human genome. He found that our DNA contains many noncoding regions in which a sequence of 10 to 100 base pairs is repeated multiple times. Although the sequence is usually the same at each region in all people, the number of times that the sequence is repeated is highly variable among individuals.nnJeffreys immediately saw the potential for forensic use of these markers, which he called “minisatellites.” In less than two years, forensic labs across the world could create DNA “fingerprints” of crime suspects by profiling their unique minisatellite makeup. For the first time, forensic scientists could create genetic profiles so specific that the only people who share them are identical twins.nnDNA fingerprint techniques evolved subtly over the next several years, until the polymerase chain reaction (PCR), developed by Kary Mullis, was introduced into forensic work. By allowing the selective amplification of any desired stretch of DNA, PCR ushered in unprecedented sensitivity in low-level DNA detection at crime scenes. All of today's forensic genetic methods are based on PCR.