Register for an account

X

Enter your name and email address below.

Your email address is used to log in and will not be shared or sold. Read our privacy policy.

X

Website access code

Enter your access code into the form field below.

If you are a Zinio, Nook, Kindle, Apple, or Google Play subscriber, you can enter your website access code to gain subscriber access. Your website access code is located in the upper right corner of the Table of Contents page of your digital edition.

Health

Native American HLAs, part II

Gene ExpressionBy Razib KhanApril 27, 2006 6:34 AM

Newsletter

Sign up for our email newsletter for the latest science news

Greg Cochran's comment below is worth turning into a post:

There's more to it than that. Tribes often have extremely limited HLA variation, contain only a small subset of the variation that you see in a wider set of Amerindians. Whereas in the old world, even little tiny groups with very low gene flow have lots of different HLA alleles. [Cavalli-Sforza 1994] You'd think that they'd lose those rare alleles by drift, but they don't - has to be frequency-dependent selection, the same force that has kept alleles around for tens of millions of years. But in the Americas, it appears that those frequency-dependent forces simply did not exist. [Slatkin and Muirhead, 2000] So, two things going on, which may or may not modify your conclusions. First, a bottleneck, probably: afterwards, a world in which HLA simply does not matter.

We talked about this subsequent to this comment. Basically in small populations subject to a lot of random genetic drift HLA diversity still remains high because stochastic factors run up against powerful negative frequency dependent selection effects. That is, the rarer the allele, the stronger its fitness advantage. So, as drift drives an allele frequency down it begins to run up against countervailing selective pressures. Just as drift is about to run an allele to extinction the break is slammed and it will "bounce back." This is why HLA variants seem to be almost immortal fragments of the genome. So what happened with Native Americans? Greg's point seems to be that Native American groups were not subject to this particular dynamic where HLA is kept diverse within groups, so convential genetic forces of drift were far more powerful on these loci than in other human groups. What's different? One could posit things like density of population, but the HLA have deep roots well before our own species.

    2 Free Articles Left

    Want it all? Get unlimited access when you subscribe.

    Subscribe

    Already a subscriber? Register or Log In

    Want unlimited access?

    Subscribe today and save 70%

    Subscribe

    Already a subscriber? Register or Log In