sentences:  The discovery of mutants that altered the period of circadian rhythms in eclosion and locomotor activity ("perS" and "perL") indicated the role of the per gene in the clock itself and not an output pathway.The period gene was first sequenced in 1984 by Michael Rosbash and colleagues.In 1998, it was discovered that "per" produces two transcripts (differing only by the alternative splicing of a single untranslated intron) which both encode the PER protein.