Osama Bin Laden is dead. At least, that's what we've been told, and I tend to believe such things.
But how do they know it's him? Well, they have the visual evidence and the body, for one. But to be certain it's not a look-a-like, the government has taken steps above and beyond to make sure they've got who they think they have: DNA analysis.
Now, I'm not entirely sure what DNA analysis has been done, but I can say this for certain - whatever method they used could be completed in a matter of hours given a lab ready to go and focused solely on this. Using commonplace PCR methods - which, for the record, is what I use in my lab every day - Bin Laden could easily be ID'd faster than you'd think. Heck, I can get DNA from a fish and turn it into sequences or genotypes in 24 hours, so I think the US government can work faster than me when time is of the essence. Allow let me explain how they could do it so quickly.
Step 1. Extract DNA
If they've got his body, then they've got enough DNA to run a billion or two genetic tests. It takes extremely little DNA to run genetic tests - on the order of single cells. So having even a 1 mm square piece of flesh would provide more DNA than they would even have use for. Extraction takes very little time. All you need to do it place the cells/tissue in some kind of solution that will break up the cell's membranes, thus liberating the DNA from the nucleus without damaging the DNA too much. There are hundreds of extraction kits and protocols. I don't know what the gov't extraction policy is, but the Arkansas State Crime Lab just uses sodium hydroxide and hydrochloric acid to extract DNA from their samples (which, btw, is how I get DNA from my fish samples, too). For example, this is their protocol for buccal punches (a.k.a. cheek tissue):
- Place 52 μl of 0.01 M NAOH in each well with 2.0 mm of tissue.
- Incubate samples at 65°C for 10 minutes.
- Add 10 μl of 0.1 M Tris HCl (pH 7.3).
- Let stand for 5 minutes.
- Samples are now ready for amplification
Step 2: Amplify Identifying DNA Sequences
Once you have DNA, you're ready to ID your suspect. While there have been a few methods used in the past, the onset of Polymerase Chain Reaction, or PCR technology, has made looking at parts of a genome pretty darn quick and easy.
The namesake of PCR, polymerase, is a very special enzyme that cells use to duplicate DNA. Polymerases are found in all creatures because we all must, at some point, have cells divide to grow and reproduce. When our cells divide, we have to make two copies of our genome - one for each new cell. To do this, our cells unwind the DNA, spread apart the two matching strands, then use each as templates to make two new strands. Polymerases are the enzymes that actually do that - they attach to single strands of DNA and grab matching nucleotides to create the other half of the strand.
PCR was invented in the 1980s and takes advantage of how our DNA reacts to temperature. At lower temperatures, like in our bodies, DNA sticks to it's complementary half and forms a tight helix. But as you turn up the heat, our DNA denatures - that is, it unwinds and each half of the helix separates. We can't use our own cell's polymerases for PCR because they can't stand that kind of heat. Instead, we've borrowed an enzyme from a particularly heat-tolerant bacteria to do the job for us.
Read the rest here.