[The molecular genetics of color blindness]

Abstract

The gene structures of three color pigments have been reported by Nathans et al. in 1985. One copy of red gene and 1 to 3 copies of green genes are tandemly repeated on X chromosome. As the structures of red and green genes are highly homologous (96%) and tandemly repeated, they cross-over on chromosome during meiosis and hybrid genes were produced. The function of these hybrid genes exhibits abnormal spectrum for red and green light. The 5' portion of the gene determines which cone cell type express the gene and the 3' portion of the gene determines the type of spectrum. In the 3' portion, exon 4 are associated with a small shift of spectrum and exon 5 determines a large shift of spectrum. For example, a hybrid gene with 5' region of red and 3' region of green is expressed in the red cones and exhibits green spectrum. Abnormality of color perception depends on the hybrid ratio of red and green genes.