Abstract
Rhythm variations have been noticed as a result of monitoring circadian fluctuations accompanying phenotypes associated with certain insect “strains.” This chapter presents the molecular biology of Drosophila clock genes. It discusses pleiotropy of per expression, germ-line transformants, and rhythms influenced by per, informational content of the period gene, and evolutionary implications of per's structure and function. The per pleiotropy, studied by monitoring the gene's temporal and spatial expression, fits loosely with the pleiotropic effects of mutations at this locus. However, there are few explicit connections between the findings that are also summarized in the chapter. For example, per expression in the heart has apparently not been detected. Another point suggested by the localization results is that fruit flies may not have their many circadian rhythms, if there are in fact lots of themcontrolled by one “master clock.”