The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

The partition of genetic distance into drift and admixture components


Anthropology, University of New Mexico

Friday 3:15-3:30, 200ABC Add to calendar

Many distinct admixed populations exist throughout the world. Population geneticists usually characterize these populations in terms of estimated ancestry from two or more source populations. This approach works as a first pass, but it ignores the action of other evolutionary forces. In particular, factors such as founder effects and small effective population size may add to the distinctiveness between admixed populations. In this study, we introduce a method to partition Nei's genetic distance between a pair of admixed populations into three components. The first component relates to differences in ancestry from source populations. The second and third components relate to genetic drift in the two admixed populations. We present a way to relate the drift components to historical events, such as founder effects. To demonstrate this novel methodology, we present computer simulations of admixture and genetic drift performed using the package SimCoal. We also apply our method to genotypes in publicly available databases. Regarding the performance of the method, we find that the component of genetic distance related to ancestral populations is highly sensitive to two issues. The first issue is ascertainment bias in marker selection. Ancestry informative markers inflate the genetic distance relative to genomic baselines. The second issue is the relatedness of the parental populations. Vastly different ancestry fractions will contribute little to the genetic distance if the source populations are closely related. Finally, we show that the drift components of genetic distance are robust to both marker sampling and the relatedness of the source populations.

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