Monday, 25 March 2013

Admixture and pigmentation in Cape Verde


The interesting thing about this paper is that it shows that one can explain skin color in people from Cape Verde better if one uses their proportion of African/European admixture, rather than by looking at individuals' genotypes at loci associated with the trait. This probably means that many loci of minor effect on the trait differentiate Europeans from Africans.
Prediction of skin color based on ancestry is much better than prediction of eye color from the same, which is not surprising since skin color is a highly polygenic trait.
PLoS Genet 9(3): e1003372. doi:10.1371/journal.pgen.1003372
Genetic Architecture of Skin and Eye Color in an African-European Admixed Population
Sandra Beleza et al.
Variation in human skin and eye color is substantial and especially apparent in admixed populations, yet the underlying genetic architecture is poorly understood because most genome-wide studies are based on individuals of European ancestry. We study pigmentary variation in 699 individuals from Cape Verde, where extensive West African/European admixture has given rise to a broad range in trait values and genomic ancestry proportions. We develop and apply a new approach for measuring eye color, and identify two major loci (HERC2[OCA2] P = 2.3×10−62, SLC24A5 P = 9.6×10−9) that account for both blue versus brown eye color and varying intensities of brown eye color. We identify four major loci (SLC24A5 P = 5.4×10−27, TYR P = 1.1×10−9, APBA2[OCA2] P = 1.5×10−8, SLC45A2 P = 6×10−9) for skin color that together account for 35% of the total variance, but the genetic component with the largest effect (~44%) is average genomic ancestry. Our results suggest that adjacent cis-acting regulatory loci for OCA2 explain the relationship between skin and eye color, and point to an underlying genetic architecture in which several genes of moderate effect act together with many genes of small effect to explain ~70% of the estimated heritability.


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