Dictionary.net

The morphological expression of genetic control of body shape. Clusters of homeotic genes control the morphology of animal body plans and body parts. Different body patterns may evolve through changes in gene number, regulation, or function. Recent evidence suggests that homeotic gene clusters were duplicated early in vertebrate evolution, but that arthropod and tetrapod diversity has largely involved regulatory changes in expression. (From Nature 1995 Aug 10;376 (6540):479-85)