Evolution of the Hox/ParaHox gene clusters.

The Hox gene cluster is a guiding force within the field of Evolutionary Developmental Biology. In large part our understanding of this gene cluster comes from only a few model organisms in developmental biology. The situation is gradually changing. A comparative review of the organisation of the Hox and ParaHox gene clusters and, in particular, instances of cluster disintegration, leads us to the view that the phenomenon of Temporal Colinearity is the major constraining force in maintaining these gene clusters over such long evolutionary timespans.