Evolution
The olfactory receptor gene family in vertebrates has been shown to evolve by birth-and-death evolution, whereby new genes within the family are created through genomic events such as gene duplications or gene conversions. Tandem duplications are evidenced by the fact that many olfactory receptor genes belonging to the same phylogenetic clade are located in the same gene cluster. Birth-and-death evolution also involves the elimination of genes from multigene family repertoires by mutations that create nonfunctional pseudogenes. The color vision priority hypothesis states that the evolution of color vision in primates may have decreased primate reliance on olfaction, which explains the relaxation of selective pressure that accounts for the accumulation of olfactory receptor pseudogenes in primates.
Read more about this topic: Olfactory Receptor
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