THThe evolution of vertebrates from invertebrate animals was an even larger evolutionary change, and it, too may have been influenced by alterations in __ and genes that regulat them. Two duplications of __ have occurred in the vertebrate lineage, and all vertebrate genomes tested to date have both of these duplications. These duplications may have been instrucmental in the origin of novel characteristics in the vertebrates. THis hypothesis remains controversial, however, in part because in addition to the __, many other genes were duplicated int eh vertebrate ancestor. Thus, the origin of novel characteristics cannot be ascribed solely to new __.
Hox genes x4