Molecular patterns and sequence polymorphisms in the red and green visual pigment genes of Japanese men

Abstract

The red-green pigment gene arrays of 203 (101 from a previous study and 102 from this study) randomly selected men of Japanese ancestry from the Seattle area were screened for the abnormal molecular patterns (deletions and red/green or green/red hybrid genes) that are usually associated with defective color vision. Such molecular patterns were found in approximately 5% of these individuals, which is equivalent to the frequency of phenotypic color vision defects in Japanese males in Japan. Thus, the majority of hybrid genes carried by Japanese males appear to be associated with defective color vision. In contrast, the frequency of hybrid genes among Caucasians and African-Americans is approximately two and five times the frequency of color vision defects in these two ethnic groups, respectively. The coding sequences of 50 males of Japanese ancestry were determined. All the polymorphisms in the red and green pigment genes that were detected in the Japanese sample had been observed in Caucasians and African-Americans. The same polymorphisms of the red pigment gene were present in the green pigment gene, suggesting that gene conversion contributes to sequence homogenization between these pigment genes. As is the case for Caucasians, exon 3 of the red and green pigment genes was observed to be a hot spot for recombination and gene conversion. Fewer polymorphic sites (4 vs 11) and haplotypes (5 vs 14) of the red pigment gene were observed in Japanese than in Caucasians. The Japanese population was more uniform with respect to the red pigment gene, with 70% of individuals having the same haplotype, as compared with the 43% for the Caucasian population. This difference was largely due to the lower degree of polymorphism at position 180 of the red pigment gene in Japanese (84% Ser and 16% Ala vs 62% Ser and 38% Ala.) The number of polymorphic sites and haplotypes in the green pigment gene was similar in the two populations. Nevertheless, the Japanese population was more uniform with 65% having the same haplotype. The difference in the frequency of alleles at position 283 accounted for this difference in haplotype distribution.