MUTATIONS IN S-CONE PIGMENT GENES AND THE ABSENCE OF COLOR-VISION IN 2 SPECIES OF NOCTURNAL PRIMATE

Most primates have short-wavelength sensitive (S) cones and one or mor e types of cone maximally sensitive in the middle to long wavelengths (M/L cones). These multiple cone types provide the basis for colour vi sion. Earlier experiments established that two species of nocturnal pr imate, the owl monkey (Aotus trivirgatus) and the bushbaby (Otolemur c rassicaudatus), lack a viable population of S cones. Because the retin as of these species have only a single type of M/L cone, they lack col our vision. Both of these species have an S-cone pigment gene that is highly homologous to the human S-cone pigment gene. Examination of the nucleotide sequences of the S-cone pigment genes reveals that each sp ecies has deleterious mutational changes: in comparison to the sequenc e for the corresponding region of the human gene, exon 4 of the bushba by S-cone pigment gene has a two nucleotide deletion and a single nucl eotide insertion that produces a frame shift and results in the introd uction of a stop codon. Exon 1 of the owl monkey S-cone pigment gene l ikewise contains deletions and insertions that produce a stop codon. T he absence of colour vision in both of these nocturnal primates can th us be traced to defects in their S-cone pigment genes.