A genetic test to tell you what "population" you are?

One of the major reasons that so much human genetic work is fixated on ascertaining the nature of population substructure is that different populations may respond differently to particular drugs. Of course population identification is only a rough proxy, but in many cases it is a good one. Years ago, Neil Risch reported the utility of genetic markers in differentiating individuals into distinct groups, and the high fidelity of these identifications with self-report. But this sort of generalization is contingent on particular conditions. In Brazil centuries of admixture have resulted in a considerable amount of gene flow between various phenotypic races. That is, Brazilians may identify as white, mixed or black, but the two ostensibly non-mixed categories often are characterized by non-trivial admixture. This means that the marginal utility of genetic tests to ascertain the individual's genetic background above & beyond their self-identification may be greater in Brazil than in ...