When we heard that Osama Bin Laden had been positively identified using DNA, we wanted to know: How did they do that so quickly?
"Forensic DNA testing can be done very quickly--in a few hours," says George Church, Professor of Genetics at Harvard Medical School and Director of the Center for Computational Genetics. (Church also heads up the Personal Genome Project, which we covered on NOVA scienceNOW back in 2008.) "Typically the protocol is PCR"--that's polymerase chain reaction, a technique for making multiple copies of a piece of DNA--"from tiny amounts of sample, followed by gel separation of DNA size variants." These "size variants," which are DNA chunks of different lengths, together create a unique "fingerprint" that can be used to identify an individual.
For a blow-by-blow account of how this all could be accomplished in under five hours, check out Christie Wilcox's excellent guest blog at Scientific American.
One recent report suggested that the purported Osama Bin Laden sample was verified against tissue from his sister, which (according to the report) had been held at Massachusetts General Hospital (MGH) after her death in Boston last year. MGH has not yet been able to confirm any piece of that story. However, Church points out, "It had been known for years that samples of a Bin Laden relative's DNA were available."
The downside of PCR, says Church, is that it is vulnerable to contamination. "One (unlikely) way that this can go wrong is if someone accidentally or intentionally contaminates the sample with overwhelming amounts of another DNA sample."
For more on DNA and its use in forensic identification, check out this primer from the Human Genome Project.