Genetic Chaos

Thursday, September 15, 2005

mtDNA Analysis of Nile River Valley Populations: A Genetic Corridor or a Barrier to Migration?

To assess the extent to which the Nile River Valley has been a corridor for human migrations between Egypt and sub-Saharan Africa, we analyzed mtDNA variation in 224 individuals from various locations along the river. Sequences of the first hypervariable segment (HV1) of the mtDNA control region and a polymorphic HpaI site at position 3592 allowed us to designate each mtDNA as being of “northern” or “southern” affiliation. Proportions of northern and southern mtDNA differed significantly between Egypt, Nubia, and the southern Sudan. At slowly evolving sites within HV1, northern-mtDNA diversity was highest in Egypt and lowest in the southern Sudan, and southern-mtDNA diversity was highest in the southern Sudan and lowest in Egypt, indicating that migrations had occurred bidirectionally along the Nile River Valley. Egypt and Nubia have low and similar amounts of divergence for both mtDNA types, which is consistent with historical evidence for long-term interactions between Egypt and Nubia. Spatial autocorrelation analysis demonstrates a smooth gradient of decreasing genetic similarity of mtDNA types as geographic distance between sampling localities increases, strongly suggesting gene flow along the Nile, with no evident barriers.We conclude that these migrations probably occurred within the past few hundred to few thousand years and that the migration from north to south was either earlier or lesser in the extent of gene flow than the migration from south to north.

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Explanation of the Pattern of P49a,f TaqI RFLP Y-Chromosome Variation in Egypt

The possible factors involved in the generation of the p49a,f TaqI Y-chromosome spatial diversity in Egypt are explored. The object is to consider explanations beyond those that emphasize gene flow mediated via military campaigns within the Nile corridor during the dynastic period. Current patterns of the most common variants (V, XI, IV) have been suggested to relate to Middle Kingdom and New Kingdom political actions in Nubia, including sometimes settler colonization, and the conquest of Egypt by Napata (in upper Nubia, northern Sudan) that initiated Dynasty XXV. Other events or processes have not been presented. However, a synthesis of evidence from archaeology, historical linguistics, texts, the distribution of haplotypes outside of Egypt, and some demographic considerations, lends greater support to the establishment, before the Middle Kingdom, of the observed distributions of the most prevalent haplotypes: V, XI, and IV. It is suggested that the pattern of diversity for these variants in the Egyptian Nile Valley, was largely the product of population events that occurred in the late Pleistocene to mid-Holocene through Dynasty I, and was sustained by continuous smaller scale bi- directional migrations/interactions. The higher frequency of V in Ethiopia than in Nubia or upper (southern) Egypt, has to be taken into account in any discussion of variation in the Nile Valley, especially in the context of the findings of historical linguistics.

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