homeobox A nucleotide sequence containing about 180 base pairs, which are identical or very similar in many eukaryotic organisms, that encodes a series of amino acids known as a homeodomain. Present in many eukaryotic regulatory proteins, this domain is an important region involved in the binding of regulatory proteins to the DNA molecule. A homeobox was first identified in the homeotic genes of Drosophila and has since been found in the homeotic genes of many animals (including humans) and in plants.

homeobox (homoeobox) In an embryo, a family of genes that cause the embryo to subdivide as it grows, to form groups of cells which will develop into particular organs and tissues.