Figure 2From: Differential regulation of two histidine ammonia-lyase genes during Xenopus development implicates distinct functions during thyroid hormone-induced formation of adult stem cells Phylogenetic tree of HALs from different species as shown in Figure 1 suggests that the two HAL genes were duplicated after the separation of mammals and amphibians but prior to the separation of Xenopus laevis and Xenopus tropicalis or that mammals lost the HAL1 gene during evolution. Back to article page