The Bovine Type I IFN Phylogenetic Tree. (A) The evolutionary history of bovine Type I IFN was inferred by using the Neighbor-Joining (NJ) method with bootstrap test (1000 replicates). The tree was rooted to IFNK and calculations were based on uniform rates of change for all sites. IFNX emerged prior to IFNA in this analysis. (B) The tree illustrates the evolutionary history of bovine IFN based on different rates of change between sites (gamma = 1). The tree was again based on the NJ method with bootstrap test (1000 replicates) and rooted to IFNK. IFNX and IFNA branched from a common ancestor in this analysis.