The rs3827760(C) allele is far more prevalent in East Asians and Native Americans than in any other population, and it is used as such in ancestry tests [PMID:22749789]. There are at least four physical characteristics that have been linked to this allele, and pretty much all in a copy-dependent manner as well (inheriting both alleles leads to a stronger expression than inheriting one):

Hair follicle thickness [PMID:18065779]

Hair straightness (i.e. lack of curliness) [PMID:23793515]

Shovel shaped incisors (teeth) [PMID:19804850]

Mammary duct branching density

A genome-wide association scan in admixed Latin Americans identifies loci influencing facial and scalp hair features

Environmental selection during the last ice age on the mother-to-infant transmission of vitamin D and fatty acids through breast milk. This article postulates that the need for more Vitamin D in higher latitudes selected for this mutation during the last ice age (~18,000 - 28,000 years ago), since it increases the branching density of mammary ducts, and just by chance the mutation also happens to lead to shovel shaped incisors.

gnxp hair thickness for asians

gnxp blog tooth shape among asians

A picture of shovel shaped incisors is at http://www.flickr.com/photos/39602184@N02/3747590190/