Who proposed 'one gene-one enzyme-one chemical reaction' theory?

Answer: Option C

Beadle and Tatum proposed the 'one gene-one enzyme-one chemical reaction' theory.
The one gene-one enzyme hypothesis is the idea that genes act through the production of enzymes, with each gene responsible for producing a single enzyme that in turn affects a single step in a metabolic pathway.
The concept was proposed by George Beadle and Edward Tatum in an influential 1941 paperon genetic mutations in the mold Neurospora crassa and subsequently was dubbed the "one gene-one enzyme hypothesis" by their collaborator Norman Horowitz.