While a person's DNA holds billions of genetic markers, criminologists look at only 15 markers to show the
molecular difference from one person to the next. They then create a
statistic that shows how likely it is that someone else might have the
same DNA profile. "If it's a nice clean profile, then the numbers are pretty incredible," indicating it's a probable match, says Ruth Ballard, California DNA expert and professor in biology at California State University, Sacramento.
But many experts agree that a partial DNA profile is much harder to evaluate. "It's those kind of samples that really end up being argued in court," says Ballard, who has served as an expert witness for prosecutors and defense attorneys on DNA evidence. "It's a rational disagreement; it's an area where experts can't decide yet." On the other hand, "If you have a full profile, and you're looking at all 15 of these markers, when you run the numbers on that, they are so incredibly low, the probability of another person having the same markers as you do is so unlikely, the crime labs are reporting it as a match," Ballard said.
Excerpted from TheSacramentoBee.com.
