Evolution of dihydropteridine reductase genes in vertebrates. (a) Maximum-likelihood phylogeny of Dhpr protein sequences based on 247 AA positions. The tree is rooted with Dhpr from urochordates. Numbers at the branches denote bootstrap values (maximum likelihood/neighbor joining) above 50%. (b) Synteny of dhpr regions in vertebrates. The human DHPR region is syntenic to two paralogons in Tetradon (Tni), stickleback (Gac), medaka (Ola) and zebrafish (Dre). Dhprb was apparently lost in Tetraodon (Tni), stickleback (Gac) and medaka (Ola) and further duplicated in zebrafish, so that two duplicates, dhprba and dhprbb, are found on chromosome 1. Numbered bars represent genes contributing to conserved synteny, genes that do not contribute to conserved synteny are not shown. Blue bars indicate genes that are also duplicated. Dotted lines connect orthologous genes.