Changes in the number of OR genes during the evolution of placental mammals. Each number in a yellow box indicates the number of intact OR genes in an extant species. Each number in a cyan oval represents the number of functional OR genes in an ancestral node estimated by the reconciled-tree method (Niimura and Nei 2007). Estimated numbers of gene gains and gene losses in each branch are also shown. Black and orange bars to the right of a species name indicate the number of gene gains and that of gene losses, respectively, compared with the 781 ancestral OR genes that were present in the MRCA of placental mammals. For example, 462 out of the 781 OR genes in the MRCA were lost in the human lineage, but 77 gene gains also occurred and resulted in the current human repertoire of 396 intact OR genes. Note that the number of gene losses in a black bar is not equal to the sum of gene losses in the branches from the MRCA to a given species, because the number of gene losses at each branch includes that of gene losses that occurred after gene duplication. For the same reason, the number of gene gains in an orange bar is not the same as the total number of gene gains in the branches from the MRCA to the species considered. The divergence time at each node was obtained from TimeTree (http://www.timetree.org/) (see Supplemental Fig. S1; Hedges et al. 2006).
