Jacob and Monod (1962) proposed a genetic hypothesis to explain the mechanism of induction and repression. The scheme of gene action pro­posed by Jacob and Monod is called the Operon Concept (operon model). Originally (as suggested by them), the operon mechanism consisted of an operator gene and a number of structural genes. As per current understand­ing however, the operon system consists of a) regulator gene, b) promoter gene, c) operator gene, d) structural gene, e) repressor, f) corepressor and g) inducer.