Evolution of Olfactory gene family. (a) Shared and specific OR genes in Visayan warty pig and six other mammalian species. (b) Phylogenetic tree constructed with OR protein sequences of Visayan warty pig showing classification of ORs in Visayan warty pig. The different family members are colored according to the colors shown in the legend of b. (c) Potential association between olfactory receptor gene and odorant recognition.