Period (gene)

Period (per) is a gene in Drosophilia which encodes a protein, PER, regulating circadian rhythm. There are some known alleles of the per gene that can make the circadian cycle longer or shorter than the usual cycle (which is around 24 hours). It is still uncertain how exactly this gene operates.

In human, there are three known PER family genes: PER1, PER2, and PER3.