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Examining the effect of natural selection on linked neutral divergence

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Version 2 2016-07-26, 01:07
Version 1 2016-07-21, 15:28
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posted on 2016-07-26, 01:07 authored by Tanya PhungTanya Phung
This is the slide for my talk that I presented this talk at The Allied Genetics Conference in Orlando, Florida in July 2016.
Abstract: A major goal in evolutionary biology is to understand the processes that shape patterns of genetic variation across genomes. One process that has received a lot of attention is natural selection. In particular, numerous studies in a variety of species have shown that neutral genetic diversity (intra-species differences) has been reduced at sites linked to those under selection. However, the effect of selection on neutral sequence divergence (inter-species differences) remains ambiguous. While some empirical studies have reported correlations between divergence and recombination which is interpreted as empirical evidence for natural selection reducing neutral linked divergence, theoretical arguments argued otherwise, especially for species that have diverged long ago. Here we address these outstanding issues by examining how natural selection has affected divergence between both closely and distantly related species. We show that neutral divergence is negatively correlated with functional content and positively correlated with estimates of background selection from primates, which is a measure of how negative selection affects linked neutral sites. These patterns persist even when comparing humans and mice, species that split 75 million years ago. Coalescent models indicate that background selection can generate these patterns, suggesting that natural selection has affected linked divergence between distantly related species. Our theoretical and simulation results show that even when the contribution of ancestral polymorphism to divergence is small, background selection in the ancestral population can still explain a large proportion of the variance in divergence across the genome. Thus, the view that selection does not affect divergence at linked neutral sites needs to be reconsidered. These findings also suggest that the effects of natural selection affecting linked neutral sites cannot be ignored when studying neutral divergence. Our work has important implications for understanding evolution of genomes and interpreting patterns of genetic variation.

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