Races do not exist, but Racism does: Why Racism is Foolish from the Perspective of Modern Genetics.
“If you ask for your DNA profile today from a company that specialized in “DNA ancestry” what you will get is essentially a picture of the “origin” of the different segments on your chromosome, so you’ll see that this segment over here (which is known to code for the following 10 genes) is African, while that segment next to it (which is known to code for the following 16 genes) is Native American. This is the obvious consequences of crossing-over, of course.
Making this fact so obvious, so front-and-center has very interesting consequences. Most importantly, it makes it clear that while one can speak of “African genes” or “Northern European genes”, one cannot extrapolate from that to an “African person”, at least not in the context of the Americas where four hundred years of random interbreeding has occurred.
All one can mean by “African person” is a less careful way of saying “person whose appearance genes are African”. It was expected that there would be substantial clustering and correlation between genes but, again in the Americas, this turns out largely not to be the case, so you may have African appearance genes, but that does not translate into an especially high probability that you have African blood genes or liver protein genes or (if you insist on that sort of thing) African sport and neuro-anatomy genes. And vice versa — you may look as Euro as they come, but chances are there was at least one African somewhere in the past ten generations or so, and that African left his/her genes in you — not as a diluted out “1024th of the blood” but as very definite stretches of DNA coding for very definite proteins.
You may insist on your whiteness all you like, but when genomic medicine becomes real, and the test reveals that you carry the African version of oncoprotein 134A, are you going to demand that you be given the “Euro” version of your cancer drug, the one that attacks oncoprotein 134B?”