(a) : In $1948$, Beadle and Tatum proposed one­ gene one­enzyme hypothesis which states that a gene controls metabolic machinery of the organism through synthesis of an enzyme. This laid the foundation of biochemical genetics. Beadle and Tatum were awarded Nobel Prize in $1958$. This one gene one enzyme theory has been changed to one gene one polypeptide hypothesis proposed by Yanofsky. $i.e.$, one gene synthesizes one polypeptide and many polypeptides form one enzyme.