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Genotypes of Northeast African Populations Reflect Recent Migrations

NEW YORK (GenomeWeb) – Present-day populations in northeastern Sudan carry genetic sequences that point to past mixing with populations migrating into Africa within the last 700 years or so, according to new research by an Uppsala University-led team.

As they reported yesterday in PLOS Genetics, researchers from Sweden, Germany, and Bahrain genotyped hundreds of individuals from 18 populations in Sudan and South Sudan, combining these profiles with documented SNP patterns in other nearby populations to explore population structure and genetic diversity in northeast Africa.

While populations in the southern part of the region, including the Nilotes, Darfur, and Kordofan populations, carried limited or negligible sequences originating in Eurasian groups, the team saw significant Eurasian ancestry in Nubian, Beja, and central Arab populations in northeast Africa. And the nature of these interactions provided a window into the region's historical population migrations and interactions.

Such admixture "largely coincides with the time of the Arab conquest, spreading in a southbound direction along the Nile and the Blue Nile," senior author Mattias Jakobsson, a researcher in the Department of Organismal Biology at Uppsala University, and his colleagues wrote. In contrast, they explained, "Nilotic populations occupying the region around the White Nile show long-term continuity, genetic isolation, and genetic links to ancestral East African people."

Jakobsson and his colleagues used Illumina Human Omni5M Exome arrays to profile nearly 4 million SNPs in 221 individuals from 18 Sudanese and South Sudanese populations. The populations spanned Afro-Asiatic, Nilo-Saharan, and Niger-Congo language families and several linguistic subgroups, they explained, and included groups with ancient ties to the region as well as groups believed to have arrived more recently.

In general, the researchers found that SNPs in these populations tended to cluster along geographic lines. But when they took a closer look at the admixture patterns in these and other nearby populations subjected to genome-wide profiling for past studies, a more complex picture emerged.

For populations in the northeast part of the region, for example, the team saw signs of ancestry corresponding to populations in Europe, the Middle East, and western Africa. While some populations appear to have mixed with local groups following their migration into the region, the group's data suggest a Copt population with ties to inhabitants of Egypt has been relatively isolated genetically from other populations in Sudan.

Populations to the south and west typically had waning Eurasian or Middle Eastern ancestry, the researchers reported. In particular, they noted that Nilotic pastoralist groups in Sudan and South Sudan had relatively modest levels of genetic differentiation. 

"The Nilotic populations have stayed largely unadmixed, which appears to be the case in Ethiopia," the authors wrote, noting that "modern-day Nilotic groups are likely direct descendants of past populations living in northeast Africa many thousands of years ago."