The genetic legacy of western Bantu migrations

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Abstract
There is little knowledge on the demographic impact of the western wave of the Bantu expansion. Only some predictions could be made based mainly on indirect archaeological, linguistic, and genetic evidences. Apart from the very limited available data on the mitochondrial DNA (mtDNA) side, there are not, however, Y-chromosome studies revealing–if any–the male contribution of western Bantu-farmers. To elucidate the still poorly characterized western Bantu expansion, we analyzed Y-chromosome (25 biallelic polymorphisms and 15 microsatellite markers) and mtDNA (hypervariable control regions I and II and selected coding region RFLPs) variation in a population of 110 individuals from southwest Africa, and compared it with a database of 2,708 Y-chromosome profiles and of 2,565 mtDNAs from all other regions of Africa. This study reveals (1) a dramatic displacement of male and female Khoisan-speaking groups in the southwest, since both the maternal and the paternal genetic pools were composed exclusively by types carried by Bantu-speakers; (2) a clear bias in the admixture process towards the mating of male Europeans with female Sub-Saharan Africans; (3) the assimilation of east African lineages by the southwest (mainly mtDNA-L3f and Y-chromosome-B2a lineages); and (4) signatures of recent male and female gene flow from the southeast into the southwest. The data also indicate that the western stream of the Bantu expansion was a more gradual process than the eastern counterpart, which likely involved multiple short dispersals.