Extreme expansion of the olfactory receptor gene repertoire in African elephants and evolutionary dynamics of orthologous gene groups in 13 placental mammals

Distribution of the total number of OR genes—(A) intact genes and (B) pseudogenes—belonging to each of the 781 OGGs found among 13 placental mammal species. Red and blue indicate Class I and Class II genes, respectively (A–F). (C) The number of intact genes was positively correlated with the number of pseudogenes belonging to the respective OGG (r = 0.731); the dashed line indicates the regression line. (D,E) Boxplots of comparison between Class I (“1”; red) and Class II (“2”; blue) OGGs for estimated numbers of gene gains and losses (D) and estimated ω values (E). (*) P < 0.05, (**) P < 0.01, and (***) P < 0.001. (F) The ω value for an OGG was positively correlated with the number of intact genes in the respective OGG (r = 0.346; P < 2.2 × 10⁻¹⁶); the dashed line indicates the regression line.