flies have extra macrochaetae on the head and notum compared to wild-type. Heterozygotes have an average of 0.29 +/- 0.07 extra macrochaetae per fly. Late third instar larval discs contain extra sensory organ precursors. Homozygotes have slightly rough eyes, due to the presence of duplicated and mispositioned bristles and occasional enlarged and irregularly shaped ommatidia. Ommatidia occasionally contain too few or extra cone cells and/or extra primary pigment cells. A small fraction of hemizygous embryos fail to hatch. These embryos show some defects in head involution and head skeleton formation, and denticle belts are sparse and disorganised.