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Wednesday, September 14, 2011

Sharp genetic discontinuity between Eastern Europe and the Caucasus


The rather artistic PCA below shows genetic clines that run through West Eurasia. It basically suggests that Europe and the Caucasus were populated by similar populations from the Near East, but didn't mix much after that. There appears to be some Russian influence among a few samples from the Caucasus, but no significant admixture from the Caucasus in Ukraine or Russia.


The Caucasus, inhabited by modern humans since the Early Upper Paleolithic and known for its linguistic diversity, is considered to be important for understanding human dispersals and genetic diversity in Eurasia. We report a synthesis of autosomal, Y chromosome and mitochondrial DNA (mtDNA) variation in populations from all major subregions and linguistic phyla of the area. Autosomal genome variation in the Caucasus reveals significant genetic uniformity among its ethnically and linguistically diverse populations, and is consistent with predominantly Near/Middle Eastern origin of the Caucasians, with minor external impacts. In contrast to autosomal and mtDNA variation, signals of regional Y chromosome founder effects distinguish the eastern from western North Caucasians. Genetic discontinuity between the North Caucasus and the East European Plain contrasts with continuity through Anatolia and the Balkans, suggesting major routes of ancient gene flows and admixture.

Bayazit Yunusbayev et al., The Caucasus as an asymmetric semipermeable barrier to ancient human migrations, Mol Biol Evol (2011) doi: 10.1093/molbev/msr221 First published online: September 13, 2011


Monday, September 5, 2011

Surprising aDNA results from Neolithic and Bronze Age Ukraine


Update 16/09/2013: The full thesis is now available to the public (see here).

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A thesis abstract published at the Grand Valley State University website reports that six out of seventeen ancient samples from Neolithic and Bronze Age Ukraine belonged to Siberian-specific mtDNA haplogroup C (see here). This looks like a very important outcome, because it suggests that East Eurasian mtDNA lineages were fairly common in pre-Indo-European Ukraine. However, they weren't found among Bronze Age Corded Ware remains from eastern Germany, with supposed origins on the Eastern Europe steppe (see here), nor are they commonly found in present-day Ukraine. So perhaps the Eastern European steppe was not the source of any large-scale migrations into Central Europe, including the Corded Ware expansions? Instead, maybe the European steppe populations were replaced by successive waves of migrants from East Central or even Central Europe? Here's the abstract, which is all that's available at the moment:


Studies of mitochondrial DNA (mtDNA) polymorphism have provided valuable insights for understanding patterns of human migration and interaction. The ability to recover ancient mtDNA sequence data from post-mortem bone and tissue samples allows us to view snapshots of historic gene pools firsthand, provided that great care is taken to prevent sample contamination. In this study, we analyzed the DNA sequence of the first hypervariable segment (HVSI) of the mtDNA control region, as well as a portion of the coding region, in 14 individuals from three collective burials from the Neolithic Dnieper-Donetz culture and three individuals from Bronze Age Kurgan burials, all located in modern-day Ukraine on the northern shores of the Black Sea (the North Pontic Region, or NPR). While most of our samples possessed mtDNA haplotypes that can be linked to European and Near Eastern populations, three Neolithic and all three Bronze Age individuals belonged to mtDNA haplogroup C, which is common in East Eurasian, particularly South Siberian, populations but exceedingly rare in Europe. Phylogeographic network analysis revealed that our samples are located at or near the ancestral node for haplogroup C and that derived lineages branching from the Neolithic samples were present in Bronze Age Kurgans. In light of the numerous examples of mtDNA admixture that can be found in both Europe and Siberia, it appears that the NPR and South Siberia are located at opposite ends of a genetic continuum established at some point prior to the Neolithic. This migration corridor may have been established during the Last Glacial Maximum due to extensive glaciation in northern Eurasia and a consequent aridization of western Asia. This implies the demographic history for the European gene pool is more complex than previously considered and also has significant implications regarding the origin of Kurgan populations.

Newton, Jeremy R., "Ancient Mitochondrial DNA From Pre-historic Southeastern Europe: The Presence of East Eurasian Haplogroups Provides Evidence of Interactions with South Siberians Across the Central Asian Steppe Belt" (2011). Masters Theses. Paper 5.