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Health

Climate adaptations & Southern Europeans are part African

Gene ExpressionBy Razib KhanApril 22, 2011 8:24 PM

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No time to blog them now...I'll get to it. But I really want to point you to two papers of interest in PLoS Genetics (all the good stuff lands on Friday!). Adaptations to Climate-Mediated Selective Pressures in Humans:

Humans inhabit a remarkably diverse range of environments, and adaptation through natural selection has likely played a central role in the capacity to survive and thrive in extreme climates. Unlike numerous studies that used only population genetic data to search for evidence of selection, here we scan the human genome for selection signals by identifying the SNPs with the strongest correlations between allele frequencies and climate across 61 worldwide populations. We find a striking enrichment of genic and nonsynonymous SNPs relative to non-genic SNPs among those that are strongly correlated with these climate variables. Among the most extreme signals, several overlap with those from GWAS, including SNPs associated with pigmentation and autoimmune diseases. Further, we find an enrichment of strong signals in gene sets related to UV radiation, infection and immunity, and cancer. Our results imply that adaptations to climate shaped the spatial distribution of variation in humans.

Climate would be "Court Jester", while immune/disease might be "Red Queen" (unless we're talking relaxation of constraint). Second, The History of African Gene Flow into Southern Europeans, Levantines, and Jews:

Previous genetic studies have suggested a history of sub-Saharan African gene flow into some West Eurasian populations after the initial dispersal out of Africa that occurred at least 45,000 years ago. However, there has been no accurate characterization of the proportion of mixture, or of its date. We analyze genome-wide polymorphism data from about 40 West Eurasian groups to show that almost all Southern Europeans have inherited 1%–3% African ancestry with an average mixture date of around 55 generations ago, consistent with North African gene flow at the end of the Roman Empire and subsequent Arab migrations. Levantine groups harbor 4%–15% African ancestry with an average mixture date of about 32 generations ago, consistent with close political, economic, and cultural links with Egypt in the late middle ages. We also detect 3%–5% sub-Saharan African ancestry in all eight of the diverse Jewish populations that we analyzed. For the Jewish admixture, we obtain an average estimated date of about 72 generations. This may reflect descent of these groups from a common ancestral population that already had some African ancestry prior to the Jewish Diasporas.

Some of the genome bloggers have found similar evidence, though more suggestive and not within a rigorous analytic framework. I have a Jewish friend whose genotype I'm running in ADMIXTURE. In lots of runs there is a small African component which I assumed was a false positive. I am curious to look at that again....

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