homeobox

A homeobox is a short, highly conserved DNA sequence of about 180 base pairs that encodes a 60-amino-acid protein domain known as the homeodomain. The homeodomain functions as a DNA-binding domain in transcription factors and is a defining feature of a large family of developmental regulators.

Genes that contain a homeobox are called homeobox-containing genes. They include the HOX genes in animals and similar families in plants and fungi. These genes are key regulators of development, helping to specify regional identities along the anterior-posterior axis and to control the formation of limbs, organs, and tissues.

In animals, many homeobox genes are organized into clusters on chromosomes (for example, the HOXA-HOXD clusters in mammals). The order of genes within a cluster often reflects their expression along the body axis, a property known as colinearity. The homeobox gene family arose early in eukaryotic evolution and has expanded by gene duplication and divergence.

Mutations in homeobox genes can cause homeotic transformations, where one body part develops with the characteristics of another. Classic examples include alterations in Drosophila antennapedia and bithorax pathways.

In research and literature, the term homeobox commonly refers to the DNA motif itself or to the broader class of homeobox-containing genes that encode homeodomains, which bind DNA and regulate transcription, contributing to developmental gene regulatory networks.