These genes are expressed in collinear spatial domains along the antero-posterior body axis and in the mesoderm they act as effectors of vertebral identity.
The sequential expression pattern of different Hox genes is often referred to as “the Hox code” (Kessel and Gruss, 1991) which, combined with different inductive properties of the genes, provides the positional information for the antero-posterior regionalization of the axial skeleton.