Final answer:
Beadle and Tatum concluded that genes encode enzymes through their experiments with the mold Neurospora crassa. They proposed the one gene-one enzyme hypothesis based on their observation of mutants in the arginine biosynthesis pathway.
Step-by-step explanation:
George Beadle and Edward Tatum concluded that genes encode enzymes through their experiments with the mold Neurospora crassa. They conducted experiments where they irradiated mold spores and observed their ability to grow on different media. By isolating mutants that required specific supplements, such as the amino acid arginine, they were able to determine that each mutant had a defect in a different gene in the arginine biosynthesis pathway. This led to the proposal of the one gene-one enzyme hypothesis, which suggests that each gene encodes one enzyme.