The chimeric L genes originally proposed to cause deuteranomaly were later found to be commonly present in men with normal color vision as well.6,9,37 To reconcile this finding with the theory that these L genes cause color blindness, Yamaguchi et al38 hypothesized that these genes are expressed in men with deuteranomaly but not in men with normal color vision. They proposed a mechanism in which only the first 2 genes in an array are expressed, and in deuteranomalous men, M genes, if present, are displaced to nonexpressed positions. To test this hypothesis, Yamaguchi et al identified 3 male eye donors with putative normal color vision who had genes for 2 L pigments. In each case, one gene specified isoleucine, alanine, and methionine at amino acid positions 230, 233, and 236, respectively, and the second gene specified threonine, serine, and valine at these respective positions. Expression of the L gene specifying threonine at position 230, serine at position 233, and valine at position 236 was not detected in total retinal messenger RNA (mRNA) from the 3 donors. This was taken as evidence that expression of the second L gene causes color blindness, and only 2 genes in an array are expressed. There is no doubt that examples can be found in which pigment genes are not expressed. However, a recent systematic characterization of the visual pigment genes expressed in retinas from men with normal color vision does not support the hypothesis that strictly 2 genes from the array are expressed.