Pattern of the divergence of olfactory receptor genes during tetrapod evolution

Abstract

The olfactory receptor (OR) multigene family is responsible for the sense of smell in vertebrate species. OR genes are scattered widely in our chromosomes and constitute one of the largest genes families in eutherian genomes. Some previous studies revealed that eutherian OR genes diverged mainly during early mammalian evolution. However, the exact period when, and the ecological reason why eutherian ORs strongly diverged has remained unclear. In this study, I peformed a strict data mining effort for marsupial opposum OR sequences and bootstrap analyses to estimate the periods of chromosomal migration and gene duplications of OR genes during tetrapod evolution. The results indicate that chromosomal mirgrations occured mainly during early vertebrate evolution before the monotreme-placental split, and that gene duplications occurred mainly during early mammalian evolution between the bird-mammal split and marsupial-placental split, coniciding with the reductiion fo opsin genes in primitive mammals. It could be through that the previous chromosomal dispersal allowed the OR genes to subsequently expand easily, and the nocturnal adaptation of early mammals might have triggered the OR gene exopansion. © 2008 Takushi Kishida.