Abstract: The Hox genes as a large family of DNA-binding transcription factors are organized into clusters that are strikingly collinear with their spatial and temporal expression patterns, with each cluster containing no more than 13 different genes, and that appear to play key roles in the body plans of a wide range of metazoan species. The genes order in the cluster is highly conserved through a long evolution terms, suggesting a selective pressure on the entire cluster. A single Hox cluster containing 15 Hox genes is found in chor- date such as amphioxus (Branchiostomafloridae), four Hox clusters distributing on 4 chromosomes are shown in mammals and more than four Hox clusters ray in teleosts, 7 Hox clusters being in zebrafish. Study on Hox genes of fishes will help to understand the evolu- tionary dynamics and patterns of Hox genes family in the short, medium and long evolutionary time, and to explain the formation of new genes, species and genetic differentiation to maintain system stability and other aspects of the role. Therefore, evaluation of DNA sequence homology and phylogenetic relationships between species will show great significance in the conservation of biological di- versity (particularly genetic diversity) and in explanation of the course and mechanismof biological evolution.

Key words: Hox gene, homeobox gene, cluster, paralogous gene