By their experimentation using the Neurospora fungus, Beadle and Tatum were able to propose the far-reaching hypothesis that

one gene produces a specific enzyme

Explanation:

The one gene-one enzyme hypothesis states that one gene specifies the production of a specific enzyme. This concept is based on Beadle and Tatum's experiment. Beadle and Tatum irradiated Neurospora spores with X-ray in order to induce mutations, then they crossed mutant strains with non-irradiated Neurospora strains. Finally, Beadle and Tatum observed that some mutant spores would not grow without addition of arginine (Arg) residues to the culture, thereby suggesting that each gene is responsible for the synthesis of one enzyme.

links? do you have a link? i don't see anything?