The Genetic Structure and History of Africans and African Americans
African Origins
The modern human originated in Africa and subsequently spread across the globe. However, the genetic relationships among the diverse populations on the African continent have been unclear. Tishkoff et al. (p. 1035; see the cover, published online 30 April) provide a detailed genetic analysis of most major groups of African populations. The findings suggest that Africans represent 14 ancestral populations. Populations tend to be of mixed ancestry which documents historical migrations. The data mainly support but sometimes challenge proposed relationships between groups of self-identified ethnicity previously hypothesized on the basis of linguistic studies. The authors also examined populations of African Americans and individuals of mixed ancestry from Cape Town, documenting the variation and origins of admixture within these groups.
Abstract
Africa is the source of all modern humans, but characterization of genetic variation and of relationships among populations across the continent has been enigmatic. We studied 121 African populations, four African American populations, and 60 non-African populations for patterns of variation at 1327 nuclear microsatellite and insertion/deletion markers. We identified 14 ancestral population clusters in Africa that correlate with self-described ethnicity and shared cultural and/or linguistic properties. We observed high levels of mixed ancestry in most populations, reflecting historical migration events across the continent. Our data also provide evidence for shared ancestry among geographically diverse hunter-gatherer populations (Khoesan speakers and Pygmies). The ancestry of African Americans is predominantly from Niger-Kordofanian (~71%), European (~13%), and other African (~8%) populations, although admixture levels varied considerably among individuals. This study helps tease apart the complex evolutionary history of Africans and African Americans, aiding both anthropological and genetic epidemiologic studies.
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Science
Volume 324 | Issue 5930
22 May 2009
22 May 2009
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Copyright © 2009, American Association for the Advancement of Science.
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Submission history
Received: 13 February 2009
Accepted: 17 April 2009
Published in print: 22 May 2009
Acknowledgments
We thank the thousands of people who donated DNA samples used in this study. We thank D. Bygott, S. J. Deo, D. Guracha, J. Hanby, D. Kariuki, P. Lufungulo, A. Mabulla, A. A. Mohamed, W. Ntandu, L. A. Nyindodo, C. Plowe, and A. Tibwitta for assisting with sample collection; K. Panchapakesan and L. Pfeiffer for assistance in sample preparation; S. Dobrin for assistance with genotyping; J. Giles, J. Bartlett, N. Kodaman, and J. Jarvis for assistance with analyses; and N. Rosenberg, J. Pritchard, A. Brooks, J. S. Friedlaender, J. Jarvis, C. Lambert, B. Payseur, N. Patterson, and J. Plotkin for helpful suggestions and discussions. Conducted in part using the ACCRE computing facility at Vanderbilt University, Nashville, TN. Supported by L. S. B. Leakey and Wenner Gren Foundation grants, NSF grants BCS-0196183, BSC-0552486, and BCS-0827436, NIH grants R01GM076637 and 1R01GM083606-01, and David and Lucile Packard and Burroughs Wellcome Foundation Career Awards (S.A.T.); NIH grant F32HG03801 (F.A.R.); and NIH grant R01 HL65234 (S.M.W. and J.H.M.). Genotyping was supported by the NHLBI Mammalian Genotyping Service. The content of this publication does not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. government. The project included in this manuscript has been funded in part with federal funds from the National Cancer Institute under contract N01-CO-12400. Original genotype data are available at http://research.marshfieldclinic.org/genetics/genotypingData_Statistics/humanDiversityPanel.asp. Data used for analyses in the current manuscript are available at www.med.upenn.edu/tishkoff/Supplemental/files.html and at http://chgr.mc.vanderbilt.edu/page/supplementary-data.
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