 The Hox genes specify somites as a whole based on their position along the anterior-posterior axis through specifying the pre-somitic mesoderm before somitogenesis occurs.After somites are made, their identity as a whole has already been determined, as is shown by the fact that transplantation of somites from one region to a completely different region results in the formation of structures usually observed in the original region.In contrast, the cells within each somite retain plasticity (the ability to form any kind of structure) until relatively late in somitic development.