The IFITM gene-clusters of different vertebrate species contain a variety of IFITM gene numbers (Fig. 4B) . Due to incomplete genome information, the gene-cluster of some species including tree shrew, platypus and some teleosts are not determined. In zebrafish, the orthologous IFITM gene-cluster only contains IFITM5 in chromosome 25. In bird and lizard, two IFITM genes IFITM3 and IFITM5 are included in the gene-cluster. The hominid IFITM gene-clusters contain 3-4 IFITM genes, and the two rodent (mouse and rat) clusters contain five IFITM genes. In other mammals (cow, dog, horse, and elephant), gene-clusters have 4-6 IFITM or IFITM-like genes, including IFITM5 and various number of IFITM-like genes.