Genetics in rhythm.

Rhythmic phenomena are widespread in biology. Genetic analysis of 24 hour circadian rhythms has a long history, and recent studies of circadian clock genes in Drosophila and Neurospora provide insight into clock mechanisms, including rhythm generation, clock setting by external signals and temperature compensation of rhythm. Faster biological rhythms, called ultradian rhythms, vary widely in periodicity and are likely to be generated by diverse mechanisms. In animals, ultradian rhythms are important in many neuromuscular systems, such as heartbeat, peristalsis and breathing. Recent progress has been made in the genetic analysis of heartbeat in humans and an ultradian rhythm controlling defecation in Caenorhabditis elegans.