The photosensitivity of a mutant circadian clock

Summary Konopka and Benzer (1971) produced a mutantDrosophila in which the circadian clock period is shortened by 20% and in which the maximum phase shift obtained from a saturating exposure of light is much increased. We examined the phase responses to lower energy exposures and found that in almost every aspect examined they are remarkably similar to those found inD. pseudoobscura, the only other fly examined in detail. In particular, theD. melanogaster mutant, unlike the wildtype, can be given an exposure of light of a critical energy at a critical phase which results in nearly complete loss of rhythmicity.We thank R. Konopka for the flies. A.T. Winfree thanks the N.S.F. for grant BMS 73 0688 and the N.I.H. for a research career development award.