Answer: C. two strains of auxotrophic Nourospora that grow on minimal medium supplemented with biotin have mutations in the same gene
Explanation: The Beadle and Tatum experiments had the exception that two strains of auxotrophic Nourospora that grow on minimal medium supplemented with biotin have mutations in the same gene. Thus they played a role in confirming the one gene, one enzyme hypothesis which is the idea that each gene encodes a single enzyme.
While correct but not exact, the hypothesis was confirmed through the use of genetic and biochemical studies of the bread mould Neurospora which were unable to make specific amino acids when mutated as a consequence of a "broken" enzyme needed to build a certain amino acid.