Recognize an individual genome from the rest. Part 3

Let’s have a look at the Y chromosome. In this case we inherited that from the father and only males have that, and the interesting point, again similar to the mitochondrial DNA, is that most of the Y chromosome does no recombine, meaning that it’s passed entire from generation to generation inherited through the male line. In this case, the Y chromosome is interesting because of course it has one main gene called SRI in which there is the base of maleness but here we could look, for forensic purposes, to the variation, the differences we may have among individuals.

Of course, this Y chromosome will be similar among the male descendants, so we are not able to disentangle the differences between the Y chromosome of my father, mine and my son, because we have the same one. But from other individuals it’s very easy because there are –of course, as we have seen all over the genome– there are STRs and we have also SNPs variants of a single nucleotide. Both are being analysed and both may be of interest, the STRs are have mainly a forensic interest and SNPs have mainly a population genetic interest.

And we are going to see that again in seeing how the genome helps to reconstruct history, because we may construct the gene genealogy of the Y chromosome for each individual from all over the world and in this case again we can see the variation all over the world and interpret this variation in terms of population history. So, for example, just looking at that, it’s possible to recognize the “Out of Africa” origin of modern humans.

Moreover, all over the world they have specific sets of this tree and looking at Europe you could see that there are groups of this tree what we call usually haplogroups that are specific of given regions and this variation has been produced all over the expansions of modern [humans] around the world. The analysis of Y chromosome for forensic purposes has to rely in STRs or microsatellites. In this case we are going to have a single peak for each for each of them, because [for Y] we are not heterozygotes or have two copies, as it would be in the case of autosomes.

And in this case it’s easy to disentangle the DNA of the male from the female, and this is very important for the cases of rapes in which what we want to see is the male part in a possible mixture of fluids. In this case is possible to recognize a single male existing and it is again very easy to recognize whether a given profile set of STRs is the same as for other individuals in a population. We have seen then the technical part. But this technical part is interesting because it has to be very well established, but forensics is important because there is a way of transporting this information into social issues, into the law.

And here it’s important to recognize that there are lots of problems beyond the specific technical genetic and statistical issues. The idea is that the profiling of our genome is important in the sense that for many cases we need always when some sample is found in a given place to see whether this belong to someone already known, and this has been pushing very strongly for the existence of databases of the genetic profiles.

We’re going to talk on that in the data issues of next chapters but here we’re going to see in the interview of this chapter which are the law parts, the technical part that has to be understood by people that are not fluent in genetic terms, how to apply all that to the real world. At the very end, forensics is not only something related to genetics, because it has had a strong power to make these genetics useful for society.