Edward Lawrie Tatum (1909-1975) was an American geneticist. He attended college at the University of Chicago and received his PhD in biochemistry from the University of Wisconsin-Madison in 1934. He worked at Stanford University, where he began his collaboration with Beadle. Beadle and Tatum's key experiments involved exposing the bread mold Neurospora crassa to x-rays, causing mutations. In a series of experiments, they showed that these mutations caused changes in specific enzymes involved in metabolic pathways. These experiments, published in 1941, led them to propose a direct link between genes and enzymatic reactions, known as the "one gene, one enzyme" hypothesis. He shared half of the Nobel Prize in Physiology or Medicine in 1958 with George Wells Beadle for showing that genes control individual steps in metabolism. A heavy cigarette smoker, he died of heart failure complicated by chronic emphysema in 1975 at the age of 65.