Model for the evolution of IFITM genes in chordates. The IFITM gene (green line) in the lamprey is only a partial transcript. In some clades such as anurans, bony fish, marsupials and eutherians, there are several IFITM paralogues, presumably arising through gene duplication. Bony fish are the first class in which IFITM5 (blue line) is present, whereas IFITM10 (red line) is tetrapod-specific. Note that in the cartilaginous fishes and urodeles (for which only EST data is available), IFITM orthologues listed as not present (dotted lines) may in fact exist but have not been detected due to the lack of a comprehensive genomic database. Extensive searching of the platypus (a monotreme) genome yielded a full transcript for IFITM5, but only partial transcripts for IFITM and IFITM10. *this information is based only on EST data because a genomic database is not available.