American geneticists George W. Beadle (1903-1989) and Edward L. Tatum (1909-1975) proposed a molecular definition of a gene based on their mutation studies in spores of fungi in _____: a gene is a segment of genetic material that determines, or codes for, one enzyme: the one gene–one enzyme hypothesis. Later this concept was broadened to one gene–one polypeptide, because many genes code for a protein that is not an enzyme or for one polypeptide of a multisubunit protein. George W. Beadle and Edward L. Tatum shared the 1958 Nobel Prize in Physiology or Medicine for their discovery of the role of genes in regulating biochemical events within cells.