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pbrayInteresting article on the BBC website about upcoming changes to the FBI's DNA database.
One thing most people don't realize is that when DNA information is stored or analyzed for comparison purposes, they don't use the entire sequence. Instead they use selected markers, basically a small subset of the total DNA. Which, of course, leads to two potential problems. First, if two databases use different markers, you can't easily compare data between the two systems, a potential problem when trying to share information across jurisdictions.
The second problem is what they refer to as chance matches. The situation where a DNA match is declared based on the subset of DNA examined, when, in fact, a broader comparison would reveal that the DNA is not identical. This is the possibility that troubles forensic scientists, who are still trying to work out how much data needs to be stored in a profile in order to rule out the possibility of chance matches.
And for those who assume well this is the FBI, of course they wouldn't declare themselves certain of a match unless they were, let's not forget Brandon Mayfield. He's the Seattle lawyer whose fingerprints the FBI mistakenly matched to the terrorist bombing in Spain, an analysis which was vigorously defended by the FBI even after Spanish law enforcement declared it to be in error. Eventually Mayfield received a rare public apology from the FBI, but if this had been a strictly domestic case, rather than a high profile case that crossed borders, one wonders if the mistake would ever been caught.
One thing most people don't realize is that when DNA information is stored or analyzed for comparison purposes, they don't use the entire sequence. Instead they use selected markers, basically a small subset of the total DNA. Which, of course, leads to two potential problems. First, if two databases use different markers, you can't easily compare data between the two systems, a potential problem when trying to share information across jurisdictions.
The second problem is what they refer to as chance matches. The situation where a DNA match is declared based on the subset of DNA examined, when, in fact, a broader comparison would reveal that the DNA is not identical. This is the possibility that troubles forensic scientists, who are still trying to work out how much data needs to be stored in a profile in order to rule out the possibility of chance matches.
And for those who assume well this is the FBI, of course they wouldn't declare themselves certain of a match unless they were, let's not forget Brandon Mayfield. He's the Seattle lawyer whose fingerprints the FBI mistakenly matched to the terrorist bombing in Spain, an analysis which was vigorously defended by the FBI even after Spanish law enforcement declared it to be in error. Eventually Mayfield received a rare public apology from the FBI, but if this had been a strictly domestic case, rather than a high profile case that crossed borders, one wonders if the mistake would ever been caught.