Figure 2.

Dramatic circadian phenotypes from single amino acid changes in PER. The locomotor activity of single flies is shown for three PER variants: PER S47D (left), wild type PER (middle), and PER S47A (right). Flies were monitored in light:dark cycles for the first 3 d of the experiment, before transfer to constant darkness to reveal the free-running periods. per S47D flies have shorter than normal rhythms (∼22 h), compared with ∼23.5 h for control flies. per S47A flies have dramatically long rhythms (∼31 h). See the text for details. The data were kindly provided by Joanna Chiu.