Clock gene

A clock gene contributes to a biological timing mechanism, for example the approximately daily circadian rhythm. Its product can participate in a feedback loop whose delayed activity changes the later production or action of other clock components. The term can describe a functional class; it should not be confused with the particular gene named CLOCK.

In the foundational fly experiment, three mutations assigned to the same locus produced arrhythmic behaviour or approximately 19-hour and 28-hour rhythms. The investigators measured both emergence timing in populations and locomotor activity in individuals. This linked inherited variation to an internal timing mechanism, rather than simply to an immediate response to light. ^[ref]