sentences:  Mutations in the per gene can shorten ("perS"), lengthen ("perL"), and even abolish ("per0") the period of the circadian rhythm.The period gene and three mutants ("perS", "perL", and "per0") were isolated in an EMS mutagenesis screen by Ronald Konopka and Seymour Benzer in 1971.The "perS", "perL", and "per0" mutations were found to not complement each other, so it was concluded that the three phenotypes were due to mutations in the same gene.