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How do population genetics people define a population?
Do they define it as a layman will do? say Africans, Americans, or so? Or is there a more scientific way of doing so? For example, I think defining one's population as one's allele frequencies makes more sense, but has this point been discussed previously?
It really depends on the study and the ethnicity. Mostly they use self-defined ethnicity and often they will require that three or four grandparents are of that ethnicity. Here's some detailed info on how the ethnicity was defined for the 1000 Genomes populations. You'll see that some populations (such as ASW) require all four grandparents to identify as that ethnicity, but some (such as ACB) only need three, and the cultural sensitivities in Japan meant that JPT participants weren't questioned directly but told that the study was only interested in people with Japanese grandparents. The mixed American super-population (AMR) is an exception to this rule due to the extreme admixture of ethnicity in these regions, and is based more in geography than ethnicity – this means that the individuals had to be from the place and have grandparents from the place.
A population is defined as a group of people (or organisms of the same species) living together in a geographical region. However, for human genetic studies, it is wise to use ethnicity as well (so group of people with the same ethnic background). See here how they define population in the 1000 genomes project.
