Desert hedgehog phylogeny. A phylogenetic tree showing the relationship of the SHH, IHH, DHH, and fish desert-like genes. Each group is composed of representatives from mammalian and non-mammalian species. The mammalian DHH group (green) clusters tightly and forms a separate linage to the fish DHH-like genes (red), which are no more closely related to DHH than they are to vertebrate IHH (yellow) and SHH (blue). Hs, human; Tt, dolphin; Xt, Xenopus; Gag, chicken; Mum, mouse; Me, tammar.