Effects of dosage alterations at the per locus on the period of the circadian clock of Drosophila

The normal 24-h period of the circadian rhythms of locomotor activity and eclosion of Drosophila melanogaster is altered by changes in per gene dosage. Females with only one dose of per+ or per s (the 19-h short-period mutant allele) or per1 (the 29-h long-period mutant allele) have periods which are about 1–2 h longer than the corresponding females with 2 doses. Females with 3 doses of per+ and males with 2 doses of per+ or per s have periods which are 1/2 to 1 h shorter than the corresponding individuals without the extra dose. Males with three per+ doses have periods which are about 1.5 h shorter than wild-type males; additional per+ doses do not shorten period further. The observation that decreased per dosage lengthens period while increased dosage shortens period suggests that the long- and short-period mutations alter period by respectively decreasing and increasing per gene or gene product activity. The per+ dosage results and the complementation behavior of per s indicate that the hypermorphic phenotype of per s results from increased activity of the per s gene product rather than an overproduction of per+ product. This is the first report of such a mutant action in Drosophila.