concept

Hox genes

A family of regulatory genes that label position along the head-to-tail axis of an embryo - they build nothing themselves, but tell each region of the body whether it is head, mid-body, or tail, so the cells there construct whatever belongs at that address. Remarkably, they sit in a row on the chromosome in the same order as the body regions they govern, and this arrangement is conserved identically in a fruit fly, a mouse, and a human.