Dna Prints

Dawn Ashworth, 15, left a friend's house last July to walk to her home in Enderby, a village in England's East Midlands. She never made it. Two days | later her body was found; she had been raped and strangled. Soon after, police arrested a 17-year-old youth in connection with that killing and an earlier, similar murder.

But three months later, convinced that the suspect was innocent of both crimes, the police freed him. How could they be so sure? By using the new technique of DNA fingerprinting, which involves analyzing nuclear rather than mitochondrial DNA, they had proved that while the same person had committed the murders, the man in custody was not the culprit. This month the police began using the test on blood samples from 2,000 Midlands men, hoping that if one of them is guilty, his DNA print will give him away.

The test involves comparing the DNA of blood, semen or hair roots found at the scene with the DNA of a suspect. What makes it virtually foolproof is that no two people (other than identical twins) have the same genetic characteristics. While considering this fact in 1983, Alec Jeffreys, a geneticist at the University of Leicester in England, realized it might be the basis for an important new tool in criminal investigations. Using restriction enzymes as "scissors," he cut the DNA taken from several people into segments and arranged them into patterns that somewhat resemble the bar codes found on supermarket products. The DNA from each individual, he found, formed a unique pattern -- in effect a DNA fingerprint.

In the Midlands case, Jeffreys established that the DNA pattern of the 17- year-old suspect did not match those obtained during the murder investigations. The patterns of each of the 2,000 Midlands men will undergo similar scrutiny. But that may take a while. Each test involves a complicated series of steps over a period of 2 1/2 weeks. Still, Jeffreys believes, with further refinements, and despite the $300 price tag, the test will more than pay for itself not only in criminal investigations but in the resolution of paternity suits. Says he: "The system works beyond my wildest dreams."