DNA Identification in Criminal Courts
Thus is born the notion of DNA identification. And it was quickly realized that this DNA identification would be especially useful in legal cases, in the criminal courts. Of course, law enforcement officials over the course of many years have looked for things that uniquely identify individuals, so as to find evidence that links a criminal to the scene of a crime. In fact, 1992 was the 100th anniversary of the use of fingerprints as an identifier.
They're uniquely powerful. They are essentially unique, and there are computer databases for fingerprints that are online across the country and are used. They're great, except that for many crimes, no fingerprints are left behind. A very common example, and an important example, is rape. For property crimes you may find fingerprints, but for many violent crimes it's harder sometimes to find fingerprints. So scientists look for other markers, biological markers, for example, as you might find in a semen sample from a rape. There has been success looking for protein differences, cell surface differences, things like the HLA complex and blood groups. But in fact, the variation is nowhere near as spectacular as in fingerprints - that is, until it was possible to read DNA.
DNA gives us rich results -- and, in principle, just as detailed as a fingerprint
You might think what we do is to take a sample and just read out a DNA text in its entirety. It would be a wonderful thing if we could get that from a sample, but that is the business of the Human Genome Project, not the business of the local constabulary....yet.
So when we do DNA comparisons, we can't read all three billion letters. What is done instead is that a very small handful of sites of variation are examined. Sites of variation here on this chromosome, perhaps, or one here, or one here, and one picks enough sites of variation to be able to have enough markers of difference.