Comparison of OR gene similarity among humans, dogs, mice, pigs, and cattle by clustering analysis of OR genes on the basis of amino acid sequence similarity. The Y-axis of the upper graph shows the number of OR genes in each cluster ranging from 2 to 43 genes. The X-axis of the lower graph indicates the cluster number, with 751 clusters. The Y-axis of the lower graph indicates the percentage of OR genes of each species within the cluster. The OR genes of different species are indicated by different colors.