How Drosophila Reacts to circadian rhythm? Wild type and mutant fruit fly's were compared. Mutant strain has mutation of doubletime, it is less effective, resulting in period of 28 hours. Mutant doubletime degrades PER but much more slower than in wild type. As a result, the per gene re expression occurs later in the mutant. The resulting effect on the fruit fly's circadian rhythm is a lengthened period.