Distinctive sequence of DNA bases.
A short sequence of DNA that is 1 80 base pairs long and located in the 3′ exon of certain genes of the Drosophila fly (where they were discovered by Walter Gehring during the 1970s). In the 1980s, Jani Christian Nusslein-Volhard discovered that one homeobox was attached (in adjacent exon) to each of the genes that are responsible for embryonic development (i.e., “switched on” only in an embryo that is developing into an adult), in a wide variety of species including invertebrates, birds, and mammals. Thus, it is now possible to locate many embryonic-development genes in many species by using a DNA probe (made via a Drosophila homeobox DNA sequence) to find homeobox sequences attached to those embryonic-development genes. In such a role, the respective homeobox sequences attached to each gene are known as DNA markers.