Genes that determine the type of differentiation the cells in a specific Drosophila segment will undergo. These genes express themselves later in development than the zygotic segmentation genes. While mutations in these genes cause the deletion of certain body parts and are generally lethal, mutations of segment identity genes allow the mutants to survive but with inappropriate structures developing in specific segments. For example, a bizarre four-winged fly results if the mutation converts halteres (q.v.) to wings. The segment identity genes are located in two clusters on the right arm of chromosome 3 (the Antp complex and the bx complex). See Antennapedia, bithorax, homeotic mutations, Hox genes, metamerism, pattern specification, zygotic segmentation mutations.
Subjects: Genetics and Genomics.