sicily7E/sicily7E full mutant eye clones show normal electroretinograms (ERGs) in young flies (2 days old, reared in the dark) but after 7 days in darkness they show a 50% reduction in amplitude, and 7 day exposure to constant light leads to even larger decreases (80%) in ERG amplitude. Mutants fail to sustain ERG amplitude upon repetitive light stimulation in young animals.