A few weeks ago I speculated that the EDAR gene was responsible for variation in hair form in regards to curly vs. straight. I based this on the distribution of polymorphisms and the variation of the phenotype geographically. I was wrong. Rather, it is responsible for variation in thickness of the hair follicle. A Thick Head of Hair Is in the Genes:

...Geneticists at the University of Tokyo and several other institutions in Japan, Thailand, and Indonesia have now used the HapMap to explore why Japanese and Chinese people have thick hair: The cross-sectional area of East Asian hair fibers averages about 30% larger than that of Africans and 50% larger than that of Europeans.

The researchers started with 170 candidate genes known to be involved in hair development based on mouse studies and rare inherited human diseases...A variant in a gene called EDAR was present in 88% of the Japanese and Chinese but not at all in the two other groups. To see how this gene affected hair thickness, the researchers examined hair fiber dimensions and DNA from 186 individuals from two ethnic groups in Southeast Asia who have a variety of hair types. Hair fibers were thickest in people who have two copies of the East Asian version of EDAR.

The researchers specifically rejected the correspondence of a particular genotype on this locus to phenotypic curliness or straightness. Don't pay attention to the adaptive explanations, the literature in this area offers cold climate as the explanation for nearly all derived East Asian features. EDAR is a major nexus for a lot of developmental action. It seems that wearing a fur cap of some sort would be better insulation than thicker hair! What we do know is according to haplotter the whole region around EDAR has been slammed by selection, SLC5A7, LOC402097, SULT1C1, SULT1C2, GCC2, LIMS1, RANBP2, FLJ32745 and finally, EDAR (just type EDAR into the "gene name" text box).

Labels: Genetics