Strong Selective Sweeps on the X Chromosome in the Human-Chimpanzee Ancestor Explain Its Low Divergence.

Bibliographic Collection: 
Publication Type: Journal Article
Authors: Dutheil, Julien Y; Munch, Kasper; Nam, Kiwoong; Mailund, Thomas; Schierup, Mikkel H
Year of Publication: 2015
Journal: PLoS Genet
Volume: 11
Issue: 8
Pagination: e1005451
Date Published: 2015 Aug
Publication Language: eng
ISSN: 1553-7404
Keywords: Animals, Chromosomes, Human, X, Female, Genetic Drift, Genetic Speciation, Genetic Variation, Humans, Male, Neanderthals, Recombination, Genetic, Selection, Genetic, Species Specificity

The human and chimpanzee X chromosomes are less divergent than expected based on autosomal divergence. We study incomplete lineage sorting patterns between humans, chimpanzees and gorillas to show that this low divergence can be entirely explained by megabase-sized regions comprising one-third of the X chromosome, where polymorphism in the human-chimpanzee ancestral species was severely reduced. We show that background selection can explain at most 10% of this reduction of diversity in the ancestor. Instead, we show that several strong selective sweeps in the ancestral species can explain it. We also report evidence of population specific sweeps in extant humans that overlap the regions of low diversity in the ancestral species. These regions further correspond to chromosomal sections shown to be devoid of Neanderthal introgression into modern humans. This suggests that the same X-linked regions that undergo selective sweeps are among the first to form reproductive barriers between diverging species. We hypothesize that meiotic drive is the underlying mechanism causing these two observations.

DOI: 10.1371/journal.pgen.1005451
Alternate Journal: PLoS Genet.