Hermann Joseph Muller

Born 1890, Died 1967
(1890-1967) US geneticist and educator who discovered 1926 that mutations can be artificially induced by X-rays. This showed that mutations are nothing more than chemical changes. He was awarded the Nobel Prize for Physiology or Medicine 1946. Muller campaigned against the needless use of X-rays in diagnosis and treatment, and pressed for safety regulations to ensure that people who were regularly exposed to X-rays were adequately protected. He also opposed nuclear-bomb tests. Muller was born in New York City in 1890 and studied at Columbia, earning his B.A. in 1910 and his Ph.D. in 1916. In 1920 he joined the University of Texas, Austin, as a student of Thomas Hunt Morgan, later becoming professor of zoology. The constraints on his freedom to express his socialist political views caused him to leave the USA 1932, and from 1933 he worked at the Institute of Genetics in the USSR as a senior geneticist of the Institute of Genetics in Moscow, where he remained until 1937. But the false ideas of Trofim Lysenko began to dominate Soviet biological research; openly critical of Lysenkoism, Muller was forced to leave in 1937. After serving in the Spanish Civil War, he worked at the Institute of Animal Genetics in Edinburgh. In 1940 he returned to the USA, becoming professor of zoology at Indiana University at year 1945. In 1919 Muller found that the mutation rate was increased by heat, and that heat did not always affect both of the chromosomes in a chromosome pair. From this he concluded that mutations involved changes at the molecular or submolecular level. His method for recognizing spontaneous gene mutation led to his discovery of a technique for artificially inducing mutations by means of X rays that has since had broad theoretical and practical application. Next he experimented with X-rays as a means of inducing mutations, and by 1926 he had proved the method successful. Muller's research convinced him that almost all mutations are deleterious. In the normal course of evolution, deleterious mutants die out and the few advantageous ones survive, but he believed that if the mutation rate is too high, the number of imperfect individuals may become too large for the species as a whole to survive. Mutation is a sudden, random change in a gene, or unit of hereditary material, that can alter an inheritable characteristic. Most mutations are not beneficial, since any change in the delicate balance of an organism having a high level of adaptation to its environment tends to be disruptive. As the environment changes, however, mutations can prove advantageous and thus contribute to evolutionary change in the species. In higher animals and many higher plants a mutation may be transmitted to future generations only if it occurs in germ, or sex cell, tissue; somatic, or body cell, mutations cannot be inherited except in plants that propagate asexually . Sometimes the word mutation is used broadly to include variations resulting from aberrations of chromosomes; in chromosomal mutations the number of chromosomes may be altered, or segments of chromosomes may be lost or rearranged. Changes within single genes, called point mutations, are actual chemical changes to the structure of the constituent DNA.American geneticist best remembered for Mullers demonstration that mutations and hereditary changes can be caused by X rays striking the genes and chromosomes of living cells. His discovery of artificially induced mutations in genes had far-reaching consequences, and he was awarded the Nobel Prize for Physiology or Medicine in 1946 Nobel Prize for Physiology or Medicine in 1946