Mutations may be induced by exposure to ultraviolet rays and alpha, beta, gamma, and X radiation, by extreme changes in temperature, and by certain mutagenic chemicals such as nitrous acid, nitrogen mustard, and chemical substitutes for portions of the nucleotide subunits of genes. H. J. Muller, an American geneticist, pioneered in inducing mutations by X-ray radiation (using the fruit fly, Drosophila ) and developed a method of detecting mutations that are lethal.
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