who, after holding several professorships, went to Stanford University, where he worked with Edward Tatum (1909–75). Using moulds, they deduced that the function of genes is to control the production of enzymes, which in turn control metabolic processes. They found that mutant genes result in abnormal (and non-operative) enzymes. For this ‘one gene-one enzyme’ theory (see one gene-one polypeptide hypothesis), they were awarded the 1958 Nobel Prize in physiology or medicine.