of the skin color of modern Europeans through its Phe374Leu (rs16891982) allele that has been directly correlated with skin color variation across a range of populations. This variation is ubiquitous in European populations but extremely rare elsewhere and shows strong signs of selection. TYR The TYR gene encodes the enzyme tyrosinase, which is involved in the production of melanin from tyrosine. It has an allele, Ser192Tyr (rs1042602), found solely in 40–50% of Europeans and linked to light-colored skin in studies of South Asian and African-American populations. East Asia A number of genes known to affect skin color have alleles that show signs of positive selection in East Asian populations. Of these, only OCA2 has been directly related to skin color measurements, while DCT, MC1R and ATRN are marked as candidate genes for future study. OCA2 Oculocutaneous albinism II (OCA2) assists in the regulation of pH in melanocytes. The OCA2 gene's derived His615Arg (rs1800414) allele has been shown to account for about 8% of the skin tone difference between African and East Asian populations in studies of an East Asian population living in Toronto and a Chinese Han population. This variant is essentially restricted to East Asia, with highest frequencies in Eastern East Asia (49–63%), midrange frequencies in Southeast Asia, and the lowest frequencies in Western China and some Eastern European populations. Candidate genes A number of studies have found genes linked to human skin pigmentation that have alleles with statistically significant frequencies in Chinese and East Asian populations. While not linked to measurements of skin tone variation directly, dopachrome tautomerase (DCT or TYRP2 rs2031526), melanocortin 1 receptor (MC1R) Arg163Gln (rs885479) and attractin (ATRN) have been indicated as potential contributors to the evolution of light skin in East Asian populations. Tanning response Tanning response in humans is controlled by a variety of genes. MC1R variants Arg151Sys (rs1805007), Arg160Trp (rs1805008), Asp294Sys (rs1805009), Val60Leu (rs1805005) and Val92Met (rs2228479) have been associated with reduced tanning response in European and/or East Asian populations. These alleles show no signs of positive selection and only occur in relatively small numbers, reaching a peak in Europe with around 28% of the population having at least one allele of one of the variations. A study of self-reported tanning ability and skin type in American non-Hispanic Caucasians found that SLC24A5 Phe374Leu is significantly associated with reduced tanning ability and also associated TYR Arg402Gln (rs1126809), OCA2 Arg305Trp (rs1800401) and a 2-SNP