Homozygous Pk61C5 larvae and transheterozygous Pk61C5/Pk61CEP3091 larvae die during the second instar. Pk61C5/Pk61C4 flies are delayed in development for one day, smaller than normal and have an 18% reduction in body weight. This reduction in size and weight is primarily due to a decrease in cell size. Pk61C5/Pk61C4 male flies are almost completely sterile, although they show no obvious defect in sperm morphology or in mating behaviour. Photoreceptor cells within homozygous clones in the eye are about 30% smaller than heterozygous cells outside the clone. This phenotype is cell autonomous. The heads of mosaic flies with homozygous heads (generated using the "ey-FLP" system) are reduced in size.