Razib Khan One-stop-shopping for all of my content

October 6, 2018

The derived SNP that causes dry earwax was not found in all non-Africans

Filed under: earwax,Population genetics,rs17822931 — Razib Khan @ 11:26 am

A new paper on Chinese genomics using hundreds of thousands of low-coverage data from NIPT screenings is making some waves. I’ll probably talk about the paper at some point. But I want to highlight the frequency of rs17822931 in Han Chinese. It’s pretty incredible how high it is.

Because the derived variant SNP, which is correlated with dry flaky earwax when present in homozygote genotypes, is also associated with less body odor, it has been studied extensively by East Asian geneticists. Basically, individuals who are homozygote for the ancestral SNP, which is the norm in Europe, the Middle East, and Africa, tend to have more body odor, and in societies and contexts where this is offensive these people are subject to more ostracism in East Asia as they are a minority (some of the studies in Japan were motivated by conscripts who elicited complaints from their colleagues).

The relatively low frequency in Guangxi is to be expected. This province was Sinicized only recently. As in, the last 500 years. And it still retains a huge ethnic minority population, and many of the Han in the province likely have that ancestry. But the question still arises: why do the Han have such a high frequency of rs17822931?

Here’s a plot of frequencies:


But the ALFRED database has more details. Sardinians, Somalis, Ethiopian Jews, and Dani from the New Guinea highlands all have very low proportions or none of the derived variant. The Ethiopian Jews are about ~40% West Eurasian, due to Middle Eastern agriculturalist ancestry. Groups like the Masai also have Middle Eastern agriculturalist ancestry. I think the low frequencies of the derived variant in the Middle East are due to migration from eastern Eurasia in the relatively recent past. The frequencies of the derived variant in Europe probably came with the Ancestral North Eurasian ancestry of the steppe people. In South and Southeast Asia the frequencies are indicative of balancing selection, even if there is no such selection, while in the New World world the derived variant is at low, but appreciable frequencies.

As I mentioned in an earlier post, a 40,000 year old Siberian had the derived variant (heterozgote). I suspect the Basal Eurasians did not.

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