Structure and evolution of the polymorphic photopigment gene of the marmoset

The marmoset Callithrix jacchus jacchus, is typical of a New World monkey in exhibiting a polymorphism of photopigments in the middlewave to longwave (535-565 nm) region of the spectrum. The single X-linked opsin gene that encodes the protein component of these pigments is present in three allelic forms producing, in marmosets, pigments with maximum sensitivities at about 543, 556 and 563 nm. All male monkeys are dichromats, whereas females may be either dichromats or trichromats. A cDNA sequence corresponding to the 563 form of this gene is reported, together with partial genomic DNA sequences of exons 2, 3, 4 and 5 of all three alleles. The origin of these sequences and their divergence from the middlewave- and longwave-sensitive pigments of man is discussed from both a functional and an evolutionary standpoint.