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Mzab: Sensitive Ancestry Segment Detection
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[QUOTE]Originally posted by the lioness,: [QB] PLOS Genetics 2012 Genomic Ancestry of North Africans Supports Back-to-Africa Migrations Brenna M. Henn equal contributor, Multiple local ancestry assignment methods, including PCADMIX, require thinning genotype datasets to remove alleles in high linkage disequilibrium between populations [29], [36]; this step discards information regarding haplotype patterns that tend to be more informative than genotypes when using data biased by SNP ascertainment [37]. HAPMIX incorporates both LD information and uncertainty in phase inference for haplotypes [18], but the software is currently limited to a two-population model. Our ancestral proportions of European and sub-Saharan ancestry for many North Africans at k = 2 [Figure 1] are similar to those obtained with HAPMIX by Price et al. [18] for the HGDP Algerian Mozabites, assuming a two-population mixture of northern Europeans and Yoruba. However, our results show that increasing the number of possible ancestral populations reveals multiple, diverse ancestries [e.g. Maghrebi, Near Eastern, Nilotic] and that the proportion of sub-Saharan African assignment decreases as these other ancestries are accounted for. This decrease in assigned sub-Saharan ancestry in North African samples, from a k = 2 model, is consistent with an interpretation that Maghrebi or Near Eastern diversity that is not present in the panel populations is more likely to be assigned to the more diverse, Sub-Saharan African ancestry. Using a two-population admixture model, Price et al. [18] estimated the time of migration from sub-Saharan Africa into the Mozabites to have begun about 100 generations ago [or more]. Our results suggest that sub-Saharan African and Maghreb admixture is considerably more recent, 24–41 generations ago [and even the upper 95% CI estimate under either model is 55ga, Table 1]. The discrepancy between these two estimates may result from our incorporation of multiple source populations, our use of non-linear models to estimate migration timing and the elimination, in Price et al. [18], of individuals with megabase long African segments. [/QB][/QUOTE]
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