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Genetic Analysis of Inner Eurasians Uncovers Three Broad Admixture Clines

NEW YORK (GenomeWeb) – Inner Eurasians fall into three broad genetic groups, a new analysis has found.

A Max Planck Institute for the Science of Human History-led team of researchers analyzed genome-wide data from more than 750 individuals belonging to 60 different ethnic groups of inner Eurasia. By combining that new modern data with previously published data as well as data from ancient individuals, the researchers began to tease out the contribution of different ancestral populations to these three broad groups, as they reported today in Nature Ecology and Evolution.

"Inner Eurasia has functioned as a conduit for human migration and cultural transfer since the first appearance of modern humans in this region. As a result, we observe deep sharing of genes between Western and Eastern Eurasian populations in multiple layers," co-first author Choongwon Jeong, a group leader at Max Planck, said in a statement.

He and his colleagues collected samples from 763 people from nine inner Eurasia countries — including Armenia, Kazakhstan, and Russia — that represented the majority of the large ethnic groups in those countries. They then combined this new data with previously published data from other present-day and ancient individuals, covering more than 580,000 SNPs.

Both principal components and Admixture algorithm-based analyses uncovered three clines within this genetic data that largely also reflected east-west geographic and linguistic differences. The three clines reflected boreal forests and tundra, forest-steppes, and steppe-shrublands as well as the distribution of Uralic- and northern and southern Turkic-speaking populations.

Broadly, the cline they dubbed 'forest tundra' included Russian, Uralic, and Yenisesian speakers, while the 'steppe-forest' cline included Turkic and Mongolic speakers from the Volga and Altai-Sayan regions as well as from southern Siberia. The 'southern steppe' cline encompassed the other populations.

With allele frequency-based three-population tests and a haplotype-sharing-based Globetrotter analyses, the researchers examined source population admixture within these three inner Eurasian groups.

The steppe cline populations, they reported, have genetic ancestry similar to that of modern Tungusic speakers from the Amur River basin, which suggested to the researchers that there might be a genetic link between Altaic language speakers, which includes Turkic, Mongolic, and Tungusic language families.

For the steppe-forest cline in particular, the researchers found that a two-way admixture of Ulchi/Nganasan and Srubnaya could approximate most of those populations well, though a more complex three-way mix of Ulchi/Nganasan, Srubnaya, and additional ancient North Eurasian-related populations fit all the steppe-forest populations.

The southern steppe populations, meanwhile, don't quite fit the Ulchi and Srubnaya pattern, though the researchers noted that the addition of Chalcolithic Iranians as a third ancestry improved the fit, but still did not fully explain the data.

Likewise, only two of the tundra populations — in the Volga region — fit the Nganasan and Srubnaya model, while the other tundra populations were better reflected in a three-way model that included additional ancient North Eurasian-related populations. This, the researchers said, suggested that forest tundra populations east of the Urals might harbor genetic ancestry from ANE-ancestry-rich pre-Bronze Age gene pools.

At the same time, they noted that no modern steppe-forest cline population has ANE-ancestry beyond what mix of Bronze Age steppe and present-day Eastern Eurasian ancestry explains, suggesting that Western and Eastern Eurasian ancestry of the steppe-forest population was mostly inherited from gene flow that occurred after the Late Bronze Age.

The researchers cautioned, though, that their sampling was not geographically uniform. "It is important to organize a future study for further sampling of sparsely populated regions between the clines, for example, Central Kazakhstan or East Siberia," added senior author Johannes Krause, also from Max Planck, in a statement.