Pigmentation
razib | March 4, 2010Over the history of this weblog I have blogged about pigmentation a fair amount. The major reason is that that's where the money is; unlike height, let alone intelligence, the genetic architecture and evolutionary history of pigmentation has been elucidated with relative clarity. That is, we know roughly the number and nature of the genes which control much of the between population variation in pigmentation. And, we also have some sense of whether the variation is due to natural selection, as well the historical trajectory of the between population differences.
For example, consider the…
razib | January 7, 2010In the aughts the elucidation of human pigmentation genetics was of one the major successes of 'omic' techniques. The fact that humans exhibit some continuous variation in complexion was strongly suggestive that more than one gene was at work to generate the range of the phenotype. On the other hand pedigree based studies going back to the 1960s suggested that only a modest number of large effect genetic variants were producing the variance. Today we can say with reasonable certainty that about half a dozen genes account for almost all the between population variation in pigmentation. For…
razib | May 14, 2009One of the peculiarities of American discussion about race is that skin color is assumed to be synonymous with racial distinctions. That is, skin color is not just a trait, but it is the trait which defines between population differences. There's a reason for this, the skin is the largest organ and it is very salient. Populations with little phylogenetic relationship to each other, from India to the Pacific to Southeast Asia have been referred to as "black" by lighter-skinned populations. No population is referred to by their neighbors as those "straight hairs," to my knowledge. But another…
razib | April 27, 2009On the order of ~1 million years ago humans seem to have evolved dark skin. While light skin evolved several times, it looks like dark skin exhibits an "consensus sequence," so that all dark skinned peoples seem to have the same genetic architecture.
This chart (from Signatures of Positive Selection in Genes Associated with Human Skin Pigmentation as Revealed from Analyses of Single Nucleotide Polymorphisms) shows that when it comes to skin color related genes the populations of Bougainville Island (off the eastern coast of Papua New Guinea) and Sub-Saharan Africa are far closer than you…
razib | April 13, 2009Over at Gene Expression Classic p-ter points to an interesting paper, Genetic Architecture of Tameness in a Rat Model of Animal Domestication:
A common feature of domestic animals is tameness - i.e. they tolerate and are unafraid of human presence and handling. To gain insight into the genetic basis of tameness and aggression, we studied an intercross between two lines of rats (Rattus norvegicus) selected over more than 60 generations for increased tameness and increased aggression against humans, respectively. We measured 45 traits, including tameness and aggression, anxiety-related traits,…
razib | March 23, 2009
Richard Sturm in Human Molecular Genetics has a really good review of the current state of pigmentation genetics, with a human centric focus:
The genetic basis underlying normal variation in the pigmentary traits of skin, hair and eye colour has been the subject of intense research directed at understanding the diversity seen both between and within human populations. A combination of approaches have been used including comparative genomics of candidate genes and the identification of regions of the human genome under positive selection, together with genome-wide and specific allele…