George Wells Beadle shared the 1958 Nobel Prize for medicine or physiology with Edward L. Tatum (1909-1975) and Joshua Lederberg (1925-) for their work in the field of genetic research. Beadle and Tatum were cited for their discovery that genes act by regulating specific chemical processes, and Lederberg was honored for his detailed studies on the genetic crossing of microorganisms. Beadle's demonstration that genes affect heredity by determining enzyme structure helped lay the foundation for the field of biochemical genetics. Beadle was born on Oct. 22, 1903, on a farm near Wahoo in eastern Nebraska (about 30 miles west of Omaha). He received his B.S. (1926) and M.S. (1927) degrees from the University of Nebraska at Lincoln. From 1927 to 1931, he attended Cornell University in Ithaca, New York, working as a researcher and doing graduate work in genetics. After receiving his Ph.D. degree in genetics from Cornell University in 1931, he joined the laboratory of geneticist Thomas Hunt Morgan (1866-1945) at the California Institute of Technology at Pasadena, where he conducted studies on the fruit fly. Beadle worked with Morgan until 1935, during which time they concluded that genes must influence heredity through chemical mechanisms. In 1935, Beadle studied in Paris (France) at the Institut de Biologie Physico-Chimique and worked with the eminent geneticist Boris Ephrussi (1901-1979), whom he had met in Morgan's laboratory. They determined that certain genes in the fruit fly were responsible for specific biochemical steps in the synthesis of its optic pigment. At least two of the steps were sequential-that is, step 1 had to occur to trigger step 2. After a year of research in Paris, Beadle returned to the United States and became an assistant professor of genetics at Harvard University in Cambridge, Massachusetts. He left Harvard a year later (1937) to join the staff of Stanford University (California) as a professor of biology. There, he began working on red bread mold with Tatum, who had joined Beadle on completion of his microbiologic and biochemical studies at the University of Wisconsin in Madison. Beadle”s most important work began in 1941, when he and Tatum subjected red bread mold to x-ray irradiation. They found that each gene governed the production of one specific enzyme-the “one gene-one enzyme” concept-and that the characteristic function of the gene was to supervise the formation of a particular enzyme. They determined that all biochemical reactions in all organisms were controlled by genes in a stepwise process in which each gene controls a particular step in the reactions, that these reactions were catalyzed by enzymes, and that each gene was responsible for the synthesis of a specific enzyme. In a 1941 report entitled “Genetic Control of Biochemical Reactions in Neurospora,” Beadle and Tatum described the generation, growth, and genetic characteristics of three mutants. Their application of genetic principles to the study of the biochemistry of microorganisms opened a new field of research. It revolutionized the manufacture of penicillin (a mold product) and provided insights into many biochemical processes. In 1946, Beadle became professor and chairman of the biology division of the California Institute of Technology at Pasadena. In 1960, he was appointed chancellor of the University of Chicago (Illinois). He retired from the University of Chicago in 1968 and became director of the American Medical Association Institute for Biomedical Research, a position he held until 1970. Beadle died in Pomona, California, on June 9, 1989, at the age of 85 years. He had received many awards and honors besides the Nobel Prize, and in 1995, he was honored on a stamp issued by Guyana.