Pigementation is turning out to be one of the most tractable phenotypes for genome-wide association studies– a new paper from Decode identifies another couple loci that influence various aspects of hair and skin pigment. These add to the growing list of pigmentation genes in Europeans–I’ve not done the math, but these loci must account for some sizeable chunk of the total genetic variance in these traits.
Why has pigmentation been so amenable to mapping, while other traits like height, weight, or most diseases hover at about 2-3% of the variance explained? One possibility is that it’s because pigmentation has been subject to strong recent selection–theory predicts that the initial moves toward an new fitness optimum will be loci of large effects, while the later moves will be smaller. Perhaps since this selective pressure has been so recent, we’re still picking up those initial mutations of large effect that are still segregating in the population?