Interestingly, the majority of IR-IFITM genes from rodents do not form species-specific clusters as each of IFITM1, IFITM2 and IFITM3 clusters together in a lineage-specific manner. This clustering indicates that IR-IFITM genes have diverged into different IFITM isoforms prior to the split of rodents from other mammals. Additionally, in the lineage-specific clusters, more than one IR-IFITM gene was observed from certain species, indicating that gene duplication of IR-IFITM genes continued until after species separation of the rodents. Furthermore, rat IFITM7 clusters closely with rat IFITM3, indicating that they are a pair of duplicated genes. Similarly, mouseIFITM7, mouseIFITM1 and mouseIFITM-like3 (IFITMac) are another group of duplicated genes, suggesting that IFITM7 might have similar biological function to IFITM3 or IFITM1.