Phylogenetic relationship of the IRBP modules. A) Phylogenetic distances between various modules of Xenopus IRBP protein. The numbers at the junctions are the number of times a branch point occurred out of 100 bootstrap reiterations. The tree was rooted with module 4, the ancestral module. B) An unrooted distance tree showing the relationships between the various IRBP modules from different animals. The tree was constructed as in panel A. Even numbered modules are more closely related to each other than to odd numbered modules.