The genetic history of admixture across inner Eurasia.

The indigenous populations of inner Eurasia-a huge geographic region covering the central Eurasian steppe and the northern Eurasian taiga and tundra-harbour tremendous diversity in their genes, cultures and languages. In this study, we report novel genome-wide data for 763 individuals from Armenia, Georgia, Kazakhstan, Moldova, Mongolia, Russia, Tajikistan, Ukraine and Uzbekistan. We furthermore report additional damage-reduced genome-wide data of two previously published individuals from the Eneolithic Botai culture in Kazakhstan (~5,400 BP). We find that present-day inner Eurasian populations are structured into three distinct admixture clines stretching between various western and eastern Eurasian ancestries, mirroring geography. The Botai and more recent ancient genomes from Siberia show a decrease in contributions from so-called 'ancient North Eurasian' ancestry over time, which is detectable only in the northern-most 'forest-tundra' cline. The intermediate 'steppe-forest' cline descends from the Late Bronze Age steppe ancestries, while the 'southern steppe' cline further to the south shows a strong West/South Asian influence. Ancient genomes suggest a northward spread of the southern steppe cline in Central Asia during the first millennium BC. Finally, the genetic structure of Caucasus populations highlights a role of the Caucasus Mountains as a barrier to gene flow and suggests a post-Neolithic gene flow into North Caucasus populations from the steppe.

Is spatial distribution of the HIV-1-resistant CCR5Delta32 allele formed by ecological factors?

It has been proposed that the Delta32 mutation in the chemokine receptor gene, inducing resistance to HIV-1 and, probably, to other virus infections, has undergone selection in historical times. The frequency of this mutant allele has changed rapidly both in time (during the last two millennia) and in space (across Eurasia). We compiled a global database on Delta32 allele frequencies in 300 populations. Nearly 10 percent of them are our data on 35 East European populations analyzed here for the first time. A detailed map of Delta32 frequency distribution was constructed and statistically analysed. We found a linearly decreasing trend with a maximum in areas surrounding the Baltic and White seas. Significant correlations with ground surface temperature were revealed. However, compared with our previous results, these correlations diminished, indicating that the influence of climate on Delta32 distribution was, if anything at all, indirect. The proposed scenario includes: i) arise and initial spread of the mutation among Uralic-speaking populations; ii) a frequency increase in northeastern Europe as a result of selection and/or genetic drift; iii) secondary spread (with selection continued) due to gene flow and the migrations of northern Europeans across the globe.