Simpson’s Jurors Get Lesson In Genetic Codes Expert Details Scientific Basis Behind Identification By Dna

The O.J. Simpson trial turned into Biology 101 Monday as jurors learned about the basic DNA science behind genetic testing that prosecutors say will prove the former football hero killed his exwife and her friend.

After more than three months of testimony in the double murder trial, prosecutors are at last homing in on blood evidence at the heart of their case. But before presenting any actual test results, they began with a lesson about the fundamental genetic codes that - passed to a child from mother and father - form the “genetic blueprint” of the body.

As Simpson’s frail mother, Eunice, watched in a wheelchair during one of her few court visits, the biochemist who supervised the prosecution’s DNA testing at an independent laboratory explained that half of each person’s DNA comes from his or her parents.

“Given this information, you can distinguish a human being basically from all others,” said Robin Cotton, director of Cellmark Diagnostics Laboratory in Germantown, Md.

Founded in 1987, the laboratory that conducted prosecution testing was the first facility of its type accredited by the American Society of Crime Laboratory Directors.

With the manner of a kindly high school biology teacher, the softspoken Cotton used basic language and simple metaphors to explain that DNA is the body’s molecular alphabet.

“If a blueprint contains all information on how to build a house,” she told jurors, “the DNA contains information on how to build you.”

In previous days of plodding testimony, jury members often looked bored, but on Monday they were so intent on trying to understand the DNA lesson that they set aside their notebooks in order to concentrate on Cotton’s words.

DNA, they learned, is located in the nucleus of almost every cell in the body, packaged into double-stranded chromosomes.

Scientists can unravel the DNA, like a piece of thread, she said.

The genetic testing called Restriction Fragment Length Polymorphism, known as RFLP, focuses on the 1 percent of the DNA string that is unique to each individual.

Under this process an electric current arranges strands of DNA according to size. The strands are then X-rayed, creating an autoradiograph that looks like a bar-code arranged on transparent film. The location of the dark bars reads differently for each person.