Background Admixture occurs when previously isolated populations come together and exchange genetic material. We hypothesize that admixture can enable rapid adaptive evolution in human populations by introducing novel genetic variants (haplotypes) at intermediate frequencies, and we test this hypothesis through the analysis of whole genome sequences sampled from admixed Latin American populations in Colombia, Mexico, Peru, and Puerto Rico. Results Our screen for admixture-enabled selection relies on the identification of loci that contain more or less ancestry from a given source population than would be expected given the genome-wide ancestry frequencies. We employ a combined evidence approach to evaluate levels of ancestry enrichment at single loci across multiple populations and multiple loci that function together to encode polygenic traits. We find cross-population signals of African ancestry enrichment at the major histocompatibility locus on chromosome 6, consistent with admixture-enabled selection for enhanced adaptive immune response. Several of the human leukocyte antigen genes at this locus, such as HLA-A , HLA-DRB51 , and HLA-DRB5 , show independent evidence of positive selection prior to admixture, based on extended haplotype homozygosity in African populations. A number of traits related to inflammation, blood metabolites, and both the innate and adaptive immune system show evidence of admixture-enabled polygenic selection in Latin American populations. Conclusions The results reported here, considered together with the ubiquity of admixture in human evolution, suggest that admixture serves as a fundamental mechanism that drives rapid adaptive evolution in human populations.

中文翻译：

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美洲地区快速适应性进化的混合选择


背景 当先前分离的种群聚集在一起并交换遗传物质时，就会发生混合。我们假设混合可以通过以中等频率引入新的遗传变异（单倍型）来实现人类群体的快速适应性进化，并且我们通过分析从哥伦比亚、墨西哥、秘鲁和墨西哥的混合拉丁美洲群体中采样的全基因组序列来检验这一假设。波多黎各。结果我们对混合选择的筛选依赖于对基因座的识别，这些基因座包含更多或更少的来自给定源群体的祖先，而不是给定全基因组祖先频率的预期。我们采用组合证据方法来评估多个群体的单个基因座和共同编码多基因性状的多个基因座的祖先富集水平。我们在 6 号染色体上的主要组织相容性位点发现了非洲血统富集的跨群体信号，这与增强适应性免疫反应的混合选择相一致。该位点上的几个人类白细胞抗原基因，例如 HLA-A 、 HLA-DRB51 和 HLA-DRB5 ，根据非洲人群中扩展的单倍型纯合性，显示出混合前阳性选择的独立证据。与炎症、血液代谢物以及先天性和适应性免疫系统相关的许多特征表明，拉丁美洲人群中存在混合多基因选择的证据。结论 本文报告的结果，与人类进化中普遍存在的混合现象一起考虑，表明混合是推动人类快速适应性进化的基本机制。