Hox genes,a set of important developmental regulator gene family in organisms,are highly conservative and typically found in an organized cluster,encoding transcriptional factors which play a critical regulatory role during the embryo development of animals.Recent researches on Hox genes have shown that gene duplication,sequence variation and selective pressure play crucial roles in the origin and evolution of Hox genes.Meanwhile,regulatory elements and co-evolution also have important effects upon the evolution of Hox genes.