Recent story about Colin Pitchfork (first person convicted of rape using DNA analysis) got me wondering how this works. How is DNA coded in a way which allows you to match it up with another sample? When you look at it under a microscope or something there aren’t exactly letters and numbers for each part of it.
In: Biology
It may be different in human mess but for animals although I don’t really see a reason why, but this is how we do it for animals (I’m in the veterinary field):
While some parts of your genes have a decently even mix of A, T, G and C (I see other comments have already explained what these are so I’m not going into detail), other regions are very repetitive. Some of them are called “variable number tandem repeat” or VNTR, which is really just a complicated way to say there’s a pair of two letters repeating itself, eg ATATATATATATATATATATATAT.
Now the interesting part is that these VNTRS can vary in the amount of repeats. I might have 10 pairs of AT while you might have 15 pairs. This means that by measuring the length of these VNTRs, we can determine whether two DNA samples match up.
We can do that by cutting out the fragments of the chromosome that contains these VNTRs and measuring them using advanced machinery.
Of course it’s a little more complicated than that, and there is a bunch of statistics involved to make sure it’s not just a coincidence that two DNA samples would happen to have the same length VNTRs, but that’s the gist of it. In the end, if you consider enough VNTRs and do the math properly, you end up with a conclusion along the lines of “there is only a 0.01% chance that these two samples that have the same VNTR lengths for every VNTR we analysed, do NOT belong to the same individual”.
It’s like a genetic fingerprint!
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