Nucleotide polymorphisms upstream of the X-chromosome opsin gene array tune L:M cone ratio

In Support of the long-held idea that cone ratio is genetically determined by variation linked to the X-chromosome opsin gene locus, the present Study identified nucleotide differences in DNA segments containing regulator regions of the L and M opsin genes that are associated with significant differences in the relative number of L versus M cones. Specific haplotypes (combinations of genetic differences) were identified that correlated with high versus low L:M cone ratio. These findings are consistent with the biological principle that DNA sequence variations affect binding affinities for protein components of complexes that influence the relative probability that all L Versus M opsin gene will be silenced during development, and in turn, produce variation in the proportion of L to M cones.