Cistron

The cistron is defined by the geneticist Seymour Benzer term that describes genetic units within which mutations can not complement.

It is by definition due to phenotypic criteria genetically not further divisible. In other words: the combination of two genes on different chromosomes may, if both genes are mutated, take place no complementation, so that they apply as a separate cistron.

Cistron is thus a refinement of the gene concept.