Hox genes are an evolutionary-developmental gene family that helps control animal body plans along the head-to-tail axis.
They encode transcription factors, proteins that regulate the activity of other genes during development. In many animals, Hox genes are arranged in clusters, and their positions in a cluster often correspond broadly to where their activity occurs along the embryo’s anterior–posterior, or head-to-tail, axis.
Hox genes are found across diverse animal groups, including insects and vertebrates. Their deep evolutionary conservation helps explain how very different animals can use related genetic instructions to organize bodies with repeated regions or appendages.
Hox genes do not independently determine every anatomical feature, and they should not be confused with mitochondrial genes, which are mainly involved in energy-related functions. Changes in when and where developmental genes act can contribute to evolutionary differences in body form.