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Health

Blue eyes going extinct!!! [Passing of the great race]

Gene ExpressionBy Razib KhanApril 10, 2006 2:54 PM

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No, not really, but perhaps a British newspaper will pick up this meme and I'll be responsible for a butt-load of misinformation. You gotta get fame somehow! Anyway... Cohort effects in a genetically determined trait: eye colour among US whites:

The prevalence of blue eye colour among non-Hispanic whites in NHANES-III was 57.4% (95% CI: 50.1-64.7) for individuals born between 1899 and 1905 compared to 33.8%...for those born between 1936 and 1951. No association was found between survival and eye colour, nor was a cohort effect evident for primary ancestry. However, proportions reporting only one ancestry in census data declined with successive birth cohorts...A secular trend of

decreasing assortative mating by ancestry

is the likely explanation.

At time 1 you have blue eyes at .57, and time 2 you had it at .34. Assume random mating in time 2 in regards to eye color, so if blue eyes is recessive you have a around .6 (recessive expression needs two copies, ergo, .6X.6 ~ .34) of the alleles in the gene pool cold for "blue." Well, that's pretty much what the phenotypic frequency was at time 1, so that implies that all the blue eye genes were in the same individuals at this point (so they are expressed). In fact, time 2 is probably not totally panmictic, so I'm probably overestimating the frequency of blue eye alleles in the population. So something doesn't add up. This study suggests that 74% of the variation in eye color can be explained by one locus, OCA2.

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