Mosaic animals in which the retina is homozygous for sd-117 (generated using the "EGUF/hid" system) have normal external eye morphology but show defects in a phototaxis assay. The electroretinogram of mosaic animals in which the retina is homozygous for sd-117 has defective on/off transients. Hemizygotes die as first/second instar larvae, homozygotes die as second instar larvae.