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Genetic Closeness of the East/West African SNP population clusters (blog source)
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[QUOTE]Originally posted by Gor: [QB] Continued: "Because we do not (yet) have vast data banks of genetic data collected in every corner of the world (at least not at the disposition of scientific researchers), claims about genetic clusters of human beings—that is, about the structure found within a species of more than 7 billion people— are often based on samples that are relatively very small. Pritchard et al. (2000) tested their Structure algorithm with a sample of 72 Africans and 90 Europeans; Rosenberg et al. (2002) published an article in Science entitled “Genetic Structure of Human Populations” based on a sample of 1,056 individuals; and Paschou et al. (2007) sought to demonstrate the utility of their PCA method with a sample of 274 people. Moreover, large “sampling gaps” in the data available clearly skew the picture of human genetic diversity (Serre and Pääbo 2004:1682; see also Wilson et al. 2001:268 on the need for “geographically exhaustive” data). When Serre and Pääbo (2004) analyzed the widely used HGDP-CEPH Human Genome Diversity Cell Line Panel,2 they found not only a dearth of individuals from North Africa, for example, but a complete absence of indigenous people from North America." "Given the relatively small numbers and limited locations of human beings who have been genotyped, the distribution of individuals sampled is important for any assessment of population structure. Serre and Pääbo (2004) argued that sampling often concentrates on “the extremes of continental land masses” (p. 1680), maximizing the geographic and therefore genetic distance between individuals presumed to belong to distinct continental clusters. Without “a sampling strategy that maximizes the geographic distribution of samples and keeps similar sample size for each geographical area,” they warned, researchers risked falsely creating “apparent substructures” (Serre and Pääbo 2004:1681). In contrast, when these researchers designed a study that sampled individuals “such that their geographic distribution around the world approximates the distribution of the human population as a whole and includes areas where Africa, Asia, and Europe meet,” the pattern of genetic variation they found was “one of gradients of allele frequencies that extend over the entire world, rather than discrete clusters” (Serre and Pääbo 2004:1679-1680)." http://www.asanet.org/journals/ST/Sept14STFeature.pdf American Sociological Association 2014 [/QB][/QUOTE]
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