P{EP} insertion in the 5' untranslated region, 269bp upstream of the putative start codon.
Homozygous clones in the retina result in a mildly disorganised ommatidial pattern and a slight reduction in eye size. Females carrying homozygous germ line clones are completely sterile but occasionally lay small deformed eggs which fail to hatch.
Precise excision of the P{EP} element reverts the mutant phenotype.