Figure 4.

Evolutionary scenario proposed for the origin and evolution of the extended Hox and ParaHox gene clusters. It implies an Evx/Mox ancestor gene initially linked to the UrProtoHox gene (step 1) that gives rise after duplication to Evx and Mox genes, which is paralleled by the generation of primordial Hox and ParaHox clusters, forming a continuous array containing all the Hox-like genes (the 'coupled' Hox-like cluster; step 3). See text for details.