Members of the T-box (Tbx) gene family share a conserved domain that codes for the T-box, a sequence involved in DNA-binding and protein dimerization. The Tbx gene family is largely conserved throughout metazoan evolution, and is implicated in a variety of developmental processes ranging from the formation of germ layers to the organizational patterning of the central nervous system. In the mouse, Tbx6 is involved in both the specification and patterning of the somites along the entire length of the embryo. Specifically, Tbx6 is expressed in the primitive streak, tail bud, and presomitic mesoderm and is essential for the specification of posterior paraxial mesoderm. In the absence of Tbx6, posterior somites are replaced by ectopic neural tubes.