Molecular and Genetic Bases for the Circadian System

Circadian rhythms represent an evolutionarily conserved adaptation to the environment that can be traced back to the earliest life forms. In animals, circadian behavior can be analyzed as an integrated system beginning with genes and leading ultimately to behavioral outputs. In the last decade, the molecular mechanism of circadian clocks has been uncovered by the use of phenotype-driven (forward) genetic analysis in a number of model systems. Circadian oscillations are generated by a set of genes forming a transcriptional autoregulatory feedback loop. Here, the molecular basis of circadian rhythms and the influence of circadian mutations on sleep are reviewed.