Ancestral proportions and admixture dynamics in geographically defined African Americans living in South Carolina


Parra, EJ; Kittles, RA; Argyropoulos, G; Pfaff, CL; Hiester, K; Bonilla, C; Sylvester, N; Parrish-Gause, D; Garvey, WT; Jin, L; McKeigue, PM; Kamboh, MI; Ferrell, RE; Pollitzer, WS; Shriver, MD; (2001) Ancestral proportions and admixture dynamics in geographically defined African Americans living in South Carolina. American journal of physical anthropology, 114 (1). pp. 18-29. ISSN 0002-9483 DOI: https://doi.org/10.1002/1096-8644(200101)114:1<18::AID-AJPA1002>3.0.CO;2-2

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Abstract

We analyzed admixture in samples of six different African- American populations from South Carolina: Gullah-speaking Sea Islanders in coastal South Carolina, residents of four counties in the "Low Country" (Berkeley, Charleston, Colleton, and Dorchester) and persons living in the city of Columbia, located in central South Carolina. We used a battery of highly informative autosomal, mtDNA, and Y-chromosome markers. Two of the autosomal markers (FY and AT3) are linked and lie 22 cM apart on chromosome 1. The results of this study indicate, in accordance with previous historical, cultural, and anthropological evidence, a very low level of European admixture in the Gullah Sea Islanders (m = 3.5 +/- 0.9%). The proportion of European admixture is higher in the Low Country (m ranging between 9.9 +/- 1.8% and 14.0 +/- 1.9%), and is highest in Columbia (m = 17.7 +/- 3.1%). A sex-biased European gene flow and a small Native American contribution to the African-American gene pool are also evident in these data. We studied the pattern of pairwise allelic associations between the FY locus and the nine other autosomal markers in our samples. In the combined sample from the Low Country (N = 548), a high level of linkage disequilibrium was observed between the linked markers, FY and AT3. Additionally, significant associations were also detected between FY and 4 of the 8 unlinked markers, suggesting the existence of significant genetic structure in this population. A continuous gene flow model of admixture could explain the observed pattern of genetic structure. A test conditioning on the overall admixture of each individual showed association of ancestry between the two linked markers (FY and AT3), but not between any of the unlinked markers, as theory predicts. Thus, even in the presence of genetic structure due to continuous gene flow or some other factor, it is possible to differentiate associations due to linkage from spurious associations due to genetic structure. (C) 2001 Wiley-Liss, Inc.

Item Type: Article
Keywords: south Carolina, African Americans, admixture, admixture linkage, disequilibrium, Chromosome-specific polymorphisms, y-chromosome, 9-bp deletion, linkage disequilibrium, admixed populations, native-american, ethnic-differences, mitochondrial-dna, mtdna variation, mapping, genes, Africa, Anthropology, Physical, DNA, Mitochondrial, genetics, Europe, Female, Human, Linkage Disequilibrium, Male, Negroid Race, genetics, Population Dynamics, South Carolina, Support, U.S. Gov't, P.H.S., Y Chromosome, genetics
Faculty and Department: Faculty of Epidemiology and Population Health > Dept of Non-Communicable Disease Epidemiology
PubMed ID: 11150049
Web of Science ID: 166202100003
URI: http://researchonline.lshtm.ac.uk/id/eprint/16780

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