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July 08, 2004

Balancing selection in color blindness?

I've posted about differences between "traditional" (hunter-gatherer) and modern populations in terms of the frequency of color blindess before and its possible implications for the impact of selection against deleterious mutations in modern populations. As Greg Cochran noted, the colour blindness genes tend to mutate a lot. So in any case, I was listening to the radio when I heard about a paper to be published this September in The American Journal of Human Genetics on color blindness. You can find the archive of the show here tomorrow, about 50 minutes in. In any case, I found a press release on the research of Sarah Tishkoff and Brian Verrelli. The researchers seem to be suggesting that the high level of variation found at the red and green "opsin" genes is the result of natural selection, that is, balancing selection that favors polymorphisms, perhaps because certain combinations of alleles have a fitness advantages (this applies to women, who have two X chromosomes, and so two alleles of each gene). The authors suggest that women are more likely to be able to distinguish shades of color in comparison to the typical non-color-blind male, not a great surprise to men who have had to deal with the female penchant for color coordinating, and they suggest that it had fitness consequences in the past because of the female gathering niche. Verrelli notes in the radio interview that male and female chimps also tend to show a difference in their ability to discern various red and orange shades, with the females being far pickier about what sort of fruit they'll put in their mouths. Note that this a case where what was originally modelled as a simple recessive-dominant affect is actually more complex, with different "dominant" (that is, functioning) alleles combining to express somewhat different phenotypes.

Posted by razib at 08:13 PM