Department of Biostatistics and Epidemiology, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
PLoS One. 2011 Jan 6;6(1):e14495. doi: 10.1371/journal.pone.0014495.
The ancestry of African-descended Americans is known to be drawn from three distinct populations: African, European, and Native American. While many studies consider this continental admixture, few account for the genetically distinct sources of ancestry within Africa--the continent with the highest genetic variation. Here, we dissect the within-Africa genetic ancestry of various populations of the Americas self-identified as having primarily African ancestry using uniparentally inherited mitochondrial DNA.
We first confirmed that our results obtained using uniparentally-derived group admixture estimates are correlated with the average autosomal-derived individual admixture estimates (hence are relevant to genomic ancestry) by assessing continental admixture using both types of markers (mtDNA and Y-chromosome vs. ancestry informative markers). We then focused on the within-Africa maternal ancestry, mining our comprehensive database of published mtDNA variation (∼5800 individuals from 143 African populations) that helped us thoroughly dissect the African mtDNA pool. Using this well-defined African mtDNA variation, we quantified the relative contributions of maternal genetic ancestry from multiple W/WC/SW/SE (West to South East) African populations to the different pools of today's African-descended Americans of North and South America and the Caribbean.
Our analysis revealed that both continental admixture and within-Africa admixture may be critical to achieving an adequate understanding of the ancestry of African-descended Americans. While continental ancestry reflects gender-specific admixture processes influenced by different socio-historical practices in the Americas, the within-Africa maternal ancestry reflects the diverse colonial histories of the slave trade. We have confirmed that there is a genetic thread connecting Africa and the Americas, where each colonial system supplied their colonies in the Americas with slaves from African colonies they controlled or that were available for them at the time. This historical connection is reflected in different relative contributions from populations of W/WC/SW/SE Africa to geographically distinct Africa-derived populations of the Americas, adding to the complexity of genomic ancestry in groups ostensibly united by the same demographic label.
众所周知，非裔美国人的祖先来自三个不同的群体：非洲人、欧洲人和美洲原住民。虽然许多研究都考虑了这种大陆混合，但很少有研究考虑到非洲内部遗传上不同的祖先来源——非洲是遗传变异最高的大陆。在这里，我们使用单倍体遗传的线粒体 DNA 来剖析自我认同主要来自非洲的美洲各种人群的非洲内部遗传祖先。
我们首先通过使用两种类型的标记（线粒体 DNA 和 Y 染色体与祖先信息标记）评估大陆混合，证实了我们使用单倍体衍生的群体混合估计值获得的结果与平均常染色体衍生的个体混合估计值相关（因此与基因组祖先相关）。然后，我们专注于非洲内部的母系祖先，挖掘我们广泛的已发表线粒体 DNA 变异数据库（来自 143 个非洲人群的约 5800 个人），这有助于我们彻底剖析非洲线粒体 DNA 库。利用这种明确界定的非洲线粒体 DNA 变异，我们量化了来自多个西部到东南非（West to South East，W/WC/SW/SE）非洲人群的母系遗传祖先对当今北美和南美以及加勒比地区非洲裔美国人不同群体的相对贡献。
我们的分析表明，大陆混合和非洲内部混合对于充分了解非裔美国人的祖先都至关重要。虽然大陆祖先反映了受美洲不同社会历史实践影响的性别特异性混合过程，但非洲内部的母系祖先反映了奴隶贸易的多样化殖民历史。我们已经证实，非洲和美洲之间存在遗传联系，每个殖民系统都从他们控制的非洲殖民地或当时可供他们使用的殖民地向美洲殖民地提供奴隶。这种历史联系反映在来自 W/WC/SW/SE 非洲的不同人群对地理上不同的非洲裔美洲人群的相对贡献上，这增加了群体中基因组祖先的复杂性，这些群体表面上是由相同的人口统计标签联合在一起的。
