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Genotyping Study Explores Ethiopian Population History

NEW YORK (GenomeWeb News) – Individuals from present-day Ethiopian populations within certain language groups share genetic features with individuals from populations in Egypt, Israel, and Syria, according to an early, online study in the American Journal of Human Genetics yesterday that used genotyping to explore long-term and more recent population patterns in Ethiopia.

"We see imprints of historical events on top of much more ancient prehistoric ones that together create a region of rich culture and genetic diversity," Wellcome Trust Sanger Institute researcher Chris Tyler-Smith, the study's senior author, said in a statement.

The well-documented linguistic and cultural diversity that exists in Ethiopian populations is not surprising given the country's long history of habitation by humans and other hominins, coupled with its physical position in the Horn of Africa, researchers explained. But prior to the current study, far less was understood about the genetic past of populations living there.

"From their geographic location, it is logical to think that migration out of Africa 60,000 years ago began in either Ethiopia or Egypt," first author Luca Pagani, a researcher affiliated with the University of Cambridge and the Sanger Institute, said in a statement. "Little was previously known about the populations inhabiting the North-East African region from a genomic perspective."

By genotyping hundreds of individuals from Ethiopia and neighboring countries, the team started to sort through some of the genetic features found in 10 Ethiopian populations, exploring the history of these populations and their relationships to one another and more broadly looking for clues about past migration events out of Africa.

Though the study did offer clues to the genetic diversity and history of Ethiopian populations, its authors noted that additional research, including more comprehensive genome sequencing studies, will likely be needed to address more complex questions about the route used during human expansions from Africa to other parts of the world.

"The next step for our research has to be to sequence the entire genomes, rather than read individual letters, of both Ethiopian people and others to really understand human origins and the out-of-Africa migration," Tyler-Smith noted.

For the current study, he and his colleagues from the UK, Ethiopia, Pakistan, and Italy used Illumina Omni 1M SNP arrays to genotype 188 individuals from 10 populations in Ethiopia, along with 23 individuals from Somalia and 24 individuals from South Sudan.

Their analysis of this SNP data pointed to high genetic diversity within and between the Ethiopian populations, with genetic patterns largely coinciding with language groups in the region. Overall, though, these populations appear to be younger than populations in southern Africa.

Within the so-called Nilotic and Omotic Ethiopian language groups, the study authors reported, individuals generally had little to no non-African ancestry. On the other hand, Ethiopians from populations speaking languages classified as Semitic-Cushitic, typically showed signs of both African and non-African ancestry.

When they used haplotype patterns to tease apart stretches of African and non-African ancestry in the Ethiopian genomes from the latter group, researchers found evidence for historical admixture between African and non-African populations stretching back around 3,000 years to roughly the same time period as legendary dalliances between the Queen of Sheba and Israel's King Solomon.

"We found that some Ethiopians have [40 to 50 percent] of their genome closer to the genomes of populations outside of Africa, while the remaining half of their genome is closer to populations within the African continent," co-author Toomas Kivisild, an anthropology researcher University of Cambridge, said in a statement.

"We calculated genetic distances," he explained, "and found that these non-African regions of the genome are closest to populations in Egypt, Israel and Syria, rather than to the neighboring Yemeni and Arabs."

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