Why Eurasians aren’t very pale

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A few years ago I wondered offhand why Eurasians weren’t very pale, since East Asians and Europeans developed light skin at different loci over the past few tens of thousands of years. In hindsight the answer seems pretty obvious. I realized the solution when looking at the skin pigmentation loci in my parents’ genotypes. They’re both homozygous for the derived “light” variant of SLC24A5, but interestingly my father has more “light” alleles than my mother. This is peculiar because my mother is notably lighter complected than my father. Then I realized that there was a likelihood that my mother carried an East Asian allele which conferred light complexion, since she’s ~15% East Asian. So of course the reason that East Asian-European hybrids aren’t exceedingly pale is that pigmentation is predominantly additive in trait value effect and they’d be heterozygotes at many loci where their parental populations would be homozygotes.

On the other hand, the F2 generation might be potentially very light indeed (or dark)….

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  1. My two daughters by my Japanese (now ex-) wife are both have her skin color. So far, only the elder has children (husband is like me of blond, blue-eyed northern European ancestry), but only one of the three (fourth coming soon) has any obvious signs of Asian ancestry: facial structure somewhat Asian, complexion about halfway between that of mother and father. Of the other two, one has brown eyes and hair, with no more than perhaps a very slight hint of Asian eye structure, the other is blond with grayish-hazel eyes and looks completely northern-European. It will be interesting to see how the fourth turns out.

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