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Genetic Ancestry of Modern, Ancient Mongolian Populations Unraveled

NEW YORK (GenomeWeb) – Two separate studies have traced the genetic ancestry of Mongolian populations, one studying modern ethnic Mongolians and one studying an ancient population from Mongolia, with both noting a relationship to Native Americans.

In the first study, published today in Nature Genetics, researchers from China and elsewhere sequenced the whole genomes of 175 ethnic Mongolians, representing six tribes, to an average 21.8-fold coverage per genome. They uncovered 16.5 million variants, including 15.2 million SNPs. From this, they developed a Mongolian haplotype reference panel, which they reported improved imputation accuracy as compared to other reference panels for data from a set of 25 Mongolian individuals.

"This panel is an important and timely addition to the global catalog of human genetic variation, providing us with new insight into the genetics of present-day East Asians and laying a foundation that will allow Mongolians and related populations to benefit from precision medicine," the researchers wrote in their paper.

They also used the data they generated, alongside datasets from the 1000 Genome Project and Human Genome Diversity Project, to explore Mongolian population history. Mongolians, they found, clustered within the East Asian umbrella and were most similar to Northern Han Chinese populations. The researchers also noted that there was less differentiation between Mongolians and admixed American populations, such as Puerto Ricans and Colombians, than between Native Americans and other East Asians, indicating that this may fill the genetic gap between the two.

In an identity-by-descent analysis, the researchers found that Mongolians share a high portion of IBD segments with Finns. In an overall analysis, they found that Mongolians have about 10 percent European ancestry, while Europeans have about 12 percent Mongolian ancestry. But when then excluded Finns from that analysis, the portion of Mongolian ancestry among Europeans fell. This and other analyses suggested to the researchers that complex admixture might have taken place in northeastern Europe and Siberia.

The researchers also constructed a maximum-likelihood phylogenetic tree that showed Southeast and East Asian populations formed a sister clade to Mongolians. At the same time, the nodes representing Europeans, South Asians, and Oceanians were each sister to the clade including Siberians, East Asians, and Southeast Asians. This, they said, hints at a closer relationship between East and North Asian populations than between East and South Asian populations.

Meanwhile, a Max Planck Institute for the Science of Human History-led team sequenced the genomes of ancient individuals from northern Mongolia from either tooth or femur samples. As they reported today in the Proceedings of the National Academy of Sciences, these 22 ancient individuals dated back to the late Bronze Age, to between about 1380 BC and 975 BC.

A principal components analysis of the individuals from the burial site in Khövsgöl province and other Eurasian populations separated them by geography, first along an east-west axis, then by a north-south axis, stretching from Siberians in the north to Taiwanese in the south. The addition of Native Americans to the analysis shifted the Late Bronze Age Khövsgöl individuals away from the modern Asian populations and toward modern Native Americans. This, they noted, is in line with Late Bronze Age Khövsgöl individuals and ancient Siberians sharing more ancestry with Native American-related gene pools.

Through admixture modeling, the researchers traced the ancestry of the Khövsgöl individuals largely to an Early Bronze Age population of hunter-gatherers from the Baikal region of Siberia. Western steppe herders, meanwhile, contributed only a small portion, about 7 percent, of Khövsgöl individuals' ancestry.

As dairy pastoralism has been widely practiced among Eastern steppe populations — including Western steppe herders — the researchers investigated whether these ancient Khövsgöl individuals might have practiced it. They isolated proteins from the ancient tooth samples for mass spectrometry-based analysis, which found evidence of bovine, sheep, and goat milk consumption among seven of the nine samples.

In combination with the genetic analysis, the researchers said that this suggests dairying was adopted in the region by local hunter-gatherers, largely through cultural exchange, rather than by population replacement.

The researchers noted that ancient Khövsgöl individuals did not appear to possess the known European genetic variant linked to lactase persistence, suggesting that they might have had other microbiome- or culture-based adaptations.