MUTANTS OF THE BIOLOGICAL CLOCK IN CHLAMYDOMONAS REINHARDI

A genetic analysis of the biological clock in Chlamydomonas reinhardi has been initiated. Of six wild-type strains tested (3 mt+ and 3 mt−), five had periods close to 24 hr whereas one had a 21-hr period. Mutants with altered clock period have been isolated. The periods of 3 of these variant strains are temperature compensated. Genetic crosses involving a long-period mutant suggest that a single gene confers the long-period character, and in general clock-period length seems to be a useful phenotypic measure of alterations in the clock due to genetic differences. One phase mutant was found but its behavior was variable and the phase of the rhythm, relative to a light–dark transition which initiates the rhythm, does not seem to be reliable as a parameter of clock differences. No markers have yet been mapped.