Those in which one developmental pattern is replaced by a different, but homologous one. The homeotic mutations of Drosophila cause an organ to differentiate abnormally and to form a homologous organ that is characteristic of an adjacent segment. Three such mutations are illustrated below. (A) A frontal view of the normal head. (B) The leg-like antenna of an ssa mutant, (C) A pb mutant with its proboscis transformed into legs. (D) A bx male in which halteres are changed into winglike appendages. Bithorax was the first homeotic mutation to be discovered. Homeotic genes were subsequently shown to control segment identity and were found to contain conserved segments called homeoboxes (q.v.). Homeotic mutations in which one floral organ is replaced by another occur in plants. See Chronology, 1915, Bridges; 1978, Lewis; 1983, Hafen, Levine, and Gehring; 1984, McGinnis et al.; 1996, Krizek and Meyerowitz; Arabidopsis thaliana, bithorax, floral organ identity mutations, Hox genes, metamerism, proboscipedia, spineless-aristapedia.
Subjects: Genetics and Genomics.