ineMI05077/ineMI05077 mutants do not show on or off transients in response to light and contain oscillations superimposed on the sustained depolarizing response in electroretinogram recordings (ERGs) and have significantly reduced phototaxis compared to wild type. Mosaic flies with homozygous ineMI05077/ineMI05077 photoreceptors (but elsewhere heterozygous) show ERGs and phototaxis similar to wild type.