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Genetics and Genomics Timeline
Hermann J. Muller (1890-1967) demonstrates that X rays can induce mutations

X rays had been used in clinical medicine and for experimental purposes in physics since their discovery in 1895. But their value to genetics research only became apparent when Hermann Muller, an American geneticist, employed radioactivity to produce point mutations in the fruit fly Drosophila.

Hermann J. Muller
Muller was a member of the research team at Columbia University that, under Thomas Hunt Morgan, developed the theory of chromosomal heredity from 1910 to 1915. Like his colleagues, Muller studied mutations and sought to map genes to specific chromosomes. Unlike most other early geneticists, however, Muller was explicitly interested in the physical and chemical nature and operations of genes.

As one consequence, Muller designed experiments to test the idea that radioactive particles would affect single genes and lead to point mutations. Beginning in late 1926, while at the University of Texas, Muller subjected male fruit flies to relatively high doses of radiation, then mated them to virgin female fruit flies.

• In a few weeks' time Muller was able to artificially induce more than 100 mutations in the resulting progeny—about half the number of all mutations discovered in Drosophila over the previous fifteen years.

• Some mutations were deadly. The effects of other mutations were visible in offspring but not lethal. As Muller interpreted his results, radioactive particles passing through the chromosomes randomly affected the molecular structure of individual genes, rendering them either inoperative or altering their chemical functions.

Muller's 1927 paper, "Artificial Transmutation of the Gene," only gave a sketchy account of his data. But his speech later that year at the International Congress of Plant Sciences created a media sensation. As Muller himself recognized, genetic manipulation might someday be employed in industry, agriculture, and medicine. And the prospect that inherited traits might be intentionally changed or controlled—and applied to human beings—provoked widespread awe and admiration.

An outspoken, sometimes controversial scientist, Muller hoped that evolutionary principles could be used to improve humanity. After World War II he warned of potential dangers of radiation, and was concerned with overpopulation and the international arms race. He also supported "positive" eugenics through the use of reproductive technologies such as sperm banks and artificial insemination, but wrote that, "Any attempt to accomplish genetic improvement through dictation must be debasing and self-defeating."

Muller's insight into genes as individual molecular units was provocative and influential. His research in artificial mutagenesis both lent experimental support to the theory of natural selection and was a spur to the development of molecular biology. Muller received the Nobel Prize in Physiology or Medicine in 1946.

Muller, H. J. Artificial transmutation of the gene. Science 46, 84-87 (1927).

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