ADAPTIVE EVOLUTION OF COLOR-VISION GENES IN HIGHER PRIMATES

The intron 4 sequences of the three polymorphic alleles at the X-linke d color photopigment locus in the squirrel monkey and the marmoset rev eal that the alleles in each species are exceptionally divergent. The data further suggest either that each triallelic system has arisen ind ependently in these two New World monkey lineages, or that in each spe cies at least seven deletions and insertions (14 in the two species) i n intron 4 have been transferred acid homogenized among the alleles by gene conversion or recombination. In either case, the alleles in each species apparently have persisted more than 5 million years and proba bly have been maintained by overdominant selection.