Beyond 2/3 and 1/3: The Complex Signatures of Sex-Biased Admixture on the X Chromosome
Beyond 2/3 and 1/3: The Complex Signatures of Sex-Biased Admixture on the X Chromosome
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DOI：
10.1534/genetics.115.178509
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发表时间：
2015-09-01
期刊：
影响因子：
3.3
通讯作者：
Rosenberg, Noah A.
中科院分区：
文献类型：
--
作者：
Goldberg, Amy;Rosenberg, Noah A.
性别偏见的人口统计学是通过比较X染色体和常染色体来研究的，X染色体是遗传的性别专一性的，常染色体不是性别专一性的。人类性别偏见的一种常见形式是性别偏见的混合，其中至少一个来源种群在构成混合种群的女性和男性的比例上不同。性别偏向混合体的研究通常检查X染色体上与常染色体相关的标记的平均祖先。一个简单的框架指出，在女性和男性数量相等的群体中，三分之二的X染色体出现在女性身上，这表明X染色体的平均混合比例是女性和男性混合参数的线性组合，系数分别为2/3和1/3。将机械混合模型扩展到适应X染色体，我们证明了这种预测在混合模型中并不普遍正确，尽管它对于作为单个事件发生的混合过程是有限的。对于具有常数持续混合的模型，我们确定了X染色体的平均混合，将女性和男性X染色体上的混合与相应的常染色体值进行比较。令人惊讶的是，在重新分析非裔美国人的遗传数据以估计来自非洲和欧洲来源的性别特异性贡献时，我们发现，与X染色体上多余的非洲祖先相比，与常染色体相适应的贡献范围很广，这使得没有来自欧洲的男性偏见的贡献或没有来自非洲的女性偏见的贡献的情况发生了。
Sex-biased demography, in which parameters governing migration and population size differ between females and males, has been studied through comparisons of X chromosomes, which are inherited sex-specifically, and autosomes, which are not. A common form of sex bias in humans is sex-biased admixture, in which at least one of the source populations differs in its proportions of females and males contributing to an admixed population. Studies of sex-biased admixture often examine the mean ancestry for markers on the X chromosome in relation to the autosomes. A simple framework noting that in a population with equally many females and males, two-thirds of X chromosomes appear in females, suggests that the mean X-chromosomal admixture fraction is a linear combination of female and male admixture parameters, with coefficients 2/3 and 1/3, respectively. Extending a mechanistic admixture model to accommodate the X chromosome, we demonstrate that this prediction is not generally true in admixture models, although it holds in the limit for an admixture process occurring as a single event. For a model with constant ongoing admixture, we determine the mean X-chromosomal admixture, comparing admixture on female and male X chromosomes to corresponding autosomal values. Surprisingly, in reanalyzing African-American genetic data to estimate sex-specific contributions from African and European sources, we find that the range of contributions compatible with the excess African ancestry on the X chromosome compared to autosomes has a wide spread, permitting scenarios either without male-biased contributions from Europe or without female-biased contributions from Africa.