During the course of evolution, many genes that control the development of metazoan body plans were co-opted to exert novel functions, along with the emergence or modification of structures. Gene amplification and/or changes in the cis- regulatory modules responsible for the transcriptional activity of these genes have certainly contributed in a major way to evolution of gene functions. In some cases, these processes led to the formation of groups of adjacent genes that appear to be controlled by both global and shared mechanisms.