Mutant eyes (generated using the "EGUF" system) display morphological defects when larvae are raised on media containing 2 mmol caffeine/L and 3 mmol hydroxyurea/L. Larvae raised on 3 mmol hydroxyurea/L alone show a slightly rough eye, barely distinguishable from controls, whereas larvae raised on 2 mmol caffeine/L alone display a severe rough eye, indicating that mutants are primarily sensitive to caffeine. Larval ingestion of caffeine results in: adults with very small eyes and gross ommatidial defects; mutant eye discs that are small and exhibit patterning defects in the ommatidial preclusters; disruption to BrdU incorporation in mutant eye discs, though no gross changes in cell number are apparent; an increase in apoptotic cells anterior to the morphogenetic furrow.

Hemizygous mutants grown on 3 mmol hydroxyurea/L eclose at a similar frequency to controls, whereas hemizygous mutants raised on 2 mmol caffeine/L do not survive to adulthood and instead die during pupal stages. Hemizygous mutants are lethal when grown on concentrations of caffeine as low as 0.25 mmol/L.