9507466 The recent discovery of genes controlling the development of the animal body plan (homeobox genes) provides an opportunity to address one of the most fundamental questions in biology. That is, what mechanisms have led to the appearance of new characters or body plans that characterize major radiations in biological diversity? We understand how species adapt to environmental changes by modifying a given body plan, but we do not yet understand how a particular body plan came into existence in the first place. For example, frogs differ from related amphibians in having two ankle bones that are greatly elongated, improving jumping ability. This research will test the hypothesis that changes in expression of homeobox genes led to this morphological innovation. It will study the expression of genes in the frog limb that, in other vertebrates, control the differentiation into lower leg (long bones) and ankle (usually short bones). The results will show whether the gene responsible for lower leg elongation is active during elongation of the ankle bones of frogs, but not in other vertebrates. If so, it will show that a vertebrate character can undergo a major evolutionary change via alteration in the expression of a few developmental control genes. The results could increase understanding of genetic mechanisms, of evolutionary history and account for the rapid appearance of certain morphological innovations in the fossil record.
