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Ronald J. Konopka coauthored the 1971 identification of circadian rhythm mutants in Drosophila melanogaster with Seymour Benzer. Their screen produced arrhythmic, short-period and long-period flies. The combination showed that a mutation can alter the period of an internal timing mechanism, rather than only disabling movement altogether.^[ref]

Automatic collection measured when adults emerged, and infrared detectors measured individual locomotion. Tests in constant darkness separated free-running timing from direct light-driven activity. Mapping and complementation indicated that the three mutations affected the same functional gene on the X chromosome, providing an entry point for the genetics of biological clocks.^[ref]

Seymour Benzer helped turn the study of behavior into an experimental problem in genetics. With Ronald J. Konopka, he reported fruit-fly mutations that abolished daily rhythmicity or changed its period to approximately 19 or 28 hours. Both adult emergence and individual locomotor activity were affected.^[ref]

Flies were tested in constant darkness, while infrared monitoring recorded individual movement without imposing a daily light cycle. Persistence of altered timing under those conditions supported an internal circadian rhythm mechanism, rather than merely a different immediate response to the lamps switching on. The mutations mapped to the same functional gene on the X chromosome.^[ref]