This animation explores the behavior of fruit flies with a mutation that affects the biological clock.

Most organisms have circadian rhythms, biological processes that operate on 24-hour cycles. These rhythms are regulated by an internal timekeeping mechanism called the biological clock. The animation illustrates an experiment that recorded the daily activity patterns of Drosophila fruit flies. The resulting activity charts, or actograms, compare two types of flies: a wild-type fly with a normal biological clock, and a per S mutant fly with an altered biological clock.

Under 24-hour light-dark cycles that simulate day and night, the normal fly has a typical 24-hour rhythm. Under constant darkness, the normal fly still has a daily rhythm, but it is a little longer than 24 hours. A per S mutant fly also has a 24-hour rhythm under a 24-hour light/dark cycle but has an unusually short 19-hour rhythm under constant darkness.

This animation is a clip from a 2000 Holiday Lecture Series, Clockwork Genes: Discoveries in Biological Time. Depending on students’ background, it may be helpful to pause the animation at various points to discuss different parts of the experiment.