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Extreme selective sweeps independently targeted the X chromosomes of the great apes.

ABSTRACT: The unique inheritance pattern of the X chromosome exposes it to natural selection in a way that is different from that of the autosomes, potentially resulting in accelerated evolution. We perform a comparative analysis of X chromosome polymorphism in 10 great ape species, including humans. In most species, we identify striking megabase-wide regions, where nucleotide diversity is less than 20% of the chromosomal average. Such regions are found exclusively on the X chromosome. The regions overlap partially among species, suggesting that the underlying targets are partly shared among species. The regions have higher proportions of singleton SNPs, higher levels of population differentiation, and a higher nonsynonymous-to-synonymous substitution ratio than the rest of the X chromosome. We show that the extent to which diversity is reduced is incompatible with direct selection or the action of background selection and soft selective sweeps alone, and therefore, we suggest that very strong selective sweeps have independently targeted these specific regions in several species. The only genomic feature that we can identify as strongly associated with loss of diversity is the location of testis-expressed ampliconic genes, which also have reduced diversity around them. We hypothesize that these genes may be responsible for selective sweeps in the form of meiotic drive caused by an intragenomic conflict in male meiosis.

SUBMITTER: Nam K

PROVIDER: S-EPMC4443357 | biostudies-literature | 2015 May

REPOSITORIES: biostudies-literature

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Extreme selective sweeps independently targeted the X chromosomes of the great apes.

Nam Kiwoong K Munch Kasper K Hobolth Asger A Dutheil Julien Yann JY Veeramah Krishna R KR Woerner August E AE Hammer Michael F MF Mailund Thomas T Schierup Mikkel Heide MH

Proceedings of the National Academy of Sciences of the United States of America 20150504 20

The unique inheritance pattern of the X chromosome exposes it to natural selection in a way that is different from that of the autosomes, potentially resulting in accelerated evolution. We perform a comparative analysis of X chromosome polymorphism in 10 great ape species, including humans. In most species, we identify striking megabase-wide regions, where nucleotide diversity is less than 20% of the chromosomal average. Such regions are found exclusively on the X chromosome. The regions overlap ...[more]

PMID: 25941379

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Project description:DNA methylation is an epigenetic modification involved in regulatory processes such as cell differentiation during development, X-chromosome inactivation, genomic imprinting and susceptibility to complex diseases. These changes can be inherited through generations and likely have played an important role during human evolution. We performed a comparative analysis of CpG methylation patterns between humans and all great apes (chimpanzee, bonobo, gorilla and orangutan) on a total of 32 individuals.Our analysis identified ~1,000 genes with significantly altered methylation patterns among the great apes, including ~200 with a methylation pattern unique to humans. Analysis of genes with human-specific epigenetic patterns identified enrichments for several functional categories that are key for human-specific traits, such as advanced facial expressions or equilibrium related to bipedalism. We also found a highly significant positive correlation between the genomic distance genome-wide and the methylation levels. In a pairwise comparison, we observed that ~9% (~30,000) of CpGs assayed show significant methylation differences between human and chimpanzee, including promoter regions of 879 genes (11.9% of those tested), suggesting that epigenetic changes have occurred at high frequency during recent primate evolution and represent an important substrate for adaptive modification of genome function. Epigenetic changes among primates are highly enriched for sites showing intermediate DNA methylation levels might be related to regulatory elements, and we observed a significant relationship between changes in DNA methylation and gene expression across multiple different tissues. We also identified a significant positive relationship between the rate of coding variation within genes and alterations of promoter methylation, suggesting concerted evolution between protein sequence and gene regulation. Contrastingly, our analysis also identified scores of genes that are perfectly conserved at the amino acid level between human and chimp, yet which show significant epigenetic difference between these two species. We conclude that epigenetic alterations represent an important force during primate evolution and has been systematically under explored in evolutionary comparative genomics.

Dataset Information

Extreme selective sweeps independently targeted the X chromosomes of the great apes.

Publications

Extreme selective sweeps independently targeted the X chromosomes of the great apes.

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