When wild-type flies are moved from a LD cycle to a DD cycle, at CT12 (circadian time) there is a reduction in mating activity seen. This reduction is abolished in per⁰¹ mutants. This effect is seen if mutant females are mated with either wild-type or mutant males. If mutant males are crossed with wild-type females, no phenotype is seen.

Viable. Adult eye and optic lobes have defects. The unconnected phenotype exhibits photoreceptors that degenerate with age, disorganized muscle tissue fills the space normally occupied by optic ganglia: flies are blind. The connected phenotype exhibits photoreceptor axons that innervate the optic ganglia, structure is disorganized and distinguishable from wild type. Extensive degeneration of photoreceptor cells becomes apparent in the form of dark spots on the compound eye.

reduced viability.