Analyses of X-linked and autosomal genetic variation in population-scale whole genome sequencing

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Abstract
Alon Keinan and colleagues estimate the ratio of genetic diversity on the X chromosome to that on the autosome (X/A) on the basis of whole-genome sequencing of 69 females from the 1000 Genomes Project. They find that across populations, the X/A ratio increases with genetic distance from genes. They further find that this ratio is reduced in Europeans compared to West Africans, which may be explained by demographic history. The ratio of genetic diversity on chromosome X to that on the autosomes is sensitive to both natural selection and demography. On the basis of whole-genome sequences of 69 females, we report that whereas this ratio increases with genetic distance from genes across populations, it is lower in Europeans than in West Africans independent of proximity to genes. This relative reduction is most parsimoniously explained by differences in demographic history without the need to invoke natural selection.