Department of Biological Statistics and Computational Biology, Cornell University, Ithaca, New York, USA.
Mol Biol Evol. 2010 Oct;27(10):2312-21. doi: 10.1093/molbev/msq117. Epub 2010 May 7.
Sex-biased demographic events can result in asymmetries in female and male effective population size that can lead to different patterns of genetic variation on chromosome X than are expected based on the patterns on the autosomes. Previous studies point to a period around the time of the dispersal of anatomically modern humans out of Africa when chromosome X experienced a significant reduction in effective population size relative to the autosomes. Here, we explore whether a sex-biased demographic history could explain these observations. We use coalescent simulations to show that a model of primarily male migration during the out-of-Africa dispersal can produce the striking patterns that are observed when comparing patterns of genetic variation on the autosomes and chromosome X. The model involves a history in which after the founder population of non-Africans lost much of its genetic diversity, subsequent mostly male gene flow from an African source brought new diversity into the population. We also explore two additional models, one of sex-biased generation time and one of a substructured population during the dispersal out of Africa with primarily female migration among demes. These latter models cannot account for the magnitude of the observed reduction in chromosome X effective population size, although it is plausible that they played a more minor role in producing the striking chromosome X/autosome patterns.
性别偏向的人口统计学事件可能导致雌性和雄性有效种群大小的不对称，这可能导致 X 染色体上的遗传变异模式与常染色体上的预期模式不同。以前的研究表明，在解剖学上的现代人从非洲扩散出去的时候，X 染色体的有效种群大小相对于常染色体经历了显著的减少。在这里，我们探讨了性别偏向的人口历史是否可以解释这些观察结果。我们使用合并模拟来表明，在非洲扩散期间主要是男性迁移的模型可以产生当比较常染色体和 X 染色体上的遗传变异模式时所观察到的显著模式。该模型涉及一个历史，即在非非洲人的创始人群体失去了大部分遗传多样性之后，随后来自非洲的主要是男性的基因流将新的多样性带入了该群体。我们还探讨了另外两个模型，一个是性别偏向的世代时间模型，另一个是在非洲扩散期间具有主要是女性迁移的亚结构种群模型。这些后一种模型不能解释观察到的 X 染色体有效种群大小的减少幅度，尽管它们在产生显著的 X 染色体/常染色体模式方面可能发挥了较小的作用。
