Relationship between cone pigments and genes in deuteranomalous subjects

Nathans et al. (1986) investigated the molecular genetic basis of red-green color vision deficiencies by Southern analysis using cloned human pigment genes as probes. Results obtained from dichromats were used to develop a scheme to identify which genes encode middle-wavelength sensitive (MWS) pigments and which encode long-wavelength sensitive (LWS) pigments. According to this scheme, most deuteranomalous subjects have both normal MWS and normal LWS pigment genes in addition to ‘fusion’ pigment genes (i.e., having sequences derived from both types of normal genes). From this they proposed that deuteranomaly arises from the expression of both normal MWS and anomalous pigments in the same cones. We have examined both the cone pigment genes and the color vision of deuteranomalous subjects. The results from Southern analysis of the genes agree with those of Nathans et al. (1986). However, the results from color matching indicate that these deuteranomalous subjects do not express any significant amount of normal MWS pigment. One interpretation is that the genes in deuteranomals identified as normal MWS pigment genes actually encode LWS pigments.