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.