Phylogenetic Analyses of the Vertebrate Immunityrelated IFITM Sub-family IR-IFITM genes can be divided into two groups: one consisting of eutherian homologs and the other including homologs from metatheria and bird. We further constructed a sub-tree to show the phylogenetic relationship of 109 IR-IFITM genes from eutheria (Fig. 3) . The sequences from elephant are located on the basal position. All IR-IFITM genes from the primate lineages form a sub-clade, and those from rodents form another sub-clade. Four genes from tree shrew form a species-specific cluster located between the sub-clades of the primates and the rodents. Three mammal species, dog, horse and cow, form several species-specific IR-IFITM gene clusters, which further compose a sub-clade in accordance with the phylogeny of these three species. These suggest that IR-IFITM genes evolved via gene duplication after species separation.