OCA2, the oculocutaneous albinism gene (also known as the human P protein gene, or, DN10), is a gene associated with albinism and certain pigmentation effects in general such as eye color, skin color, and hair color.
A large (>3,000 individuals) study of Caucasians indicates that the following OCA2 variants, all located in the first intron of the gene, are preferentially linked to blue eye color inheritance; together, they form haplotypes that (in some cases at least) predict eye color with greater than 50:50 odds. [PMID 17236130]; OMIM 203200.0013
The haplotypes are defined in order as listed above for these 3 SNPs, so, for example, the TGT haplotype refers to rs745174(T)-rs6497268(G)-rs11855019(T). The correspondence between diplotypes (the two haplotypes in one individual) and the % of individuals with blue/gray, green/hazel/ and brown eye color , respectively, was reported as follows for the most common diplotypes[PMID 17236130]:
- TGT/TGT: 62.5, 28.0, 9.5
- TGT/TTC: 47.1, 20.3, 32.6
- TGT/CGT: 28.6, 14.3, 57.1
- TGT/TGC: 27.9, 22.1, 50.0
- TGC/TTC: 25.0, 8.3, 66.7
- TTT/TGC: 20.7, 31.0, 48.3
- TGT/TTT: 17.6, 38.5, 44.0
- TGT/CTC: 7.9, 23.3, 68.8
The haplotypes shown in bold italics represent the ones reported by the authors of this study to be most associated with brown eye color. Furthermore, the haplotypes shown above are as published, and the associated SNPs - which have since changed # as well - are not in the orientation shown in dbSNP.
More recently, a study of a large Danish family led to associations with 2 SNPs in a different region of OCA2 as linked to blue or brown eye color:
Earlier studies found different regions of the OCA2 gene to also be predictive of eye color;
- OCA2 SNP rs1800401 helps predict brown eye color. [PMID 12163334] [PMID 15889046]; OMIM 203200.0011]
- OCA2 SNP rs1800407 may be associated with green/hazel eye color in some populations, but not others. [PMID 12163334], [PMID 15889046]; OMIM 203200.0012 The R419Q variant of the OCA2 gene (AA at this position, reported as TT on 23andMe) may also predict a somewhat higher risk of melanoma in people of European ancestry, according to researchers in Australia. [PMID 18252222]