Аннотация:
Admixture is increasingly being recognized as an important factor in
evolutionary genetics. The distribution of genomic admixture tracts,
and the resulting effects on admixture linkage disequilibrium, can be
used to date the timing of admixture between species or populations.
However, the theory used for such prediction assumes selective neutrality
despite the fact that many famous examples of admixture involve natural
selection acting for or against admixture. In this paper, we investigate
the effects of positive selection on the distribution of tract lengths.
We develop a theoretical framework that relies on approximating the
trajectory of the selected allele using a logistic function. By numerically
calculating the expected allele trajectory, we also show that the approach
can be extended to cases where the logistic approximation is poor due to
the effects of genetic drift. Using simulations, we show that the model
is highly accurate under most scenarios. We use the model to show that
positive selection on average will tend to increase the admixture tract
length. However, perhaps counter-intuitively, conditional on the allele
frequency at the time of sampling, positive selection will actually produce
shorter expected tract lengths. We discuss the consequences of our results
in interpreting the timing of the introgression of EPAS1 from Denisovans
into the ancestors of Tibetans.
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