Photoreceptor cells of flies expressing inaD^C645S.ninaE in a inaD^T1 background show entirely wild-type quantum bump shape, latency and amplitude in response to single photons. The photoreceptors also show the same stimulus threshold for quantum bump production as wild-type cells.

Photoreceptor cells of flies carrying inaD^C645S.ninaE in a inaD^T1 background show severe defects upon stimulation with brighter light flashes. At lower light levels, the response is indistinguishable from wild type, but as the flash intensity is increased, the mutant photoreceptor cells show an inactivation defect which becomes more pronounced as the light intensity increases. This defect is due to a defect in the rate of production of quantum bumps in the mutant; the mutant photoreceptors show a bump rate that rises unattenuated for the entire light intensity range tested, whereas for wild-type photoreceptors, the bump rate rises with a shallower slope at higher light intensity than at lower light intensity.

Photoreceptor cells of flies carrying inaD^C645S.ninaE in a inaD^T1 background do not show a dip in activity when shifted from darkness to bright light, in contrast to wild-type photoreceptors.

Flies carrying inaD^C645S.ninaE in a inaD^T1 background show normal phototaxis behaviour and normal escape jump behaviour in response to a mechanical shock. However, they are severely impaired in their ability to execute an escape jump in response to sudden darkness.