43] Molecular analysis of human red/ green visual pigment gene locus: relationship to color vision

Abstract

The retina has three classes of cone photoreceptors containing blue (short wave)-, green (middle wave)-, or red (long wave)-sensitive photopigments. Retinal cones are used for vision in bright light and for color vision. The photopigments have characteristic absorption maxima with wide regions of overlap. Perception of color results from comparison between the output from the three cone photoreceptors. The high degree of homology between the red and green pigment genes (including introns and intergenic sequences) has predisposed the locus to unequal homologous recombination/gene conversion events. These illegitimate events cause a change in the number of green pigment genes (including their total elimination) and the formation of red–green hybrid genes. The presence of the red and green pigment genes on the X chromosome and their propensity for unequal recombination account for the relatively high frequency of red–green color vision defects among males. This chapter focuses on determining the gross structure, coding sequences, and expression of the red and green pigment genes.