Spineless-aristapedia: a homeotic gene that does not control the development of specific compartments in Drosophila.

A two-step screen for isolating null mutations of the spineless-aristapedia locus has been performed, and several amorphic mutations, as well as a small deficiency, have been obtained. With the exception of the deficiency, which deletes genes required for viability on either side of the spineless-aristapedia locus, these mutations result in a transformation of only the distal antenna into distal leg, thereby indicating that the spineless-aristapedia gene is required for specifying antennal as opposed to leg development in only the distal portion of the antenna. Because this distal region does not appear to be a developmental compartment, it is probable that the spineless-aristapedia gene, unlike several other homeotic genes, is required for maintaining the correct determined state in a population of cells defined by their relative position, not by their ancestry.