The production of mutations in Drosophila melanogaster by irradiation with alpha-rays
Ward, Frances Douglas
Doctor of Philosophy
The artificial transmutation of the gene is an old problem. Investigators tried to produce mutations artificially, but failed until 1927 when Muller announced that gene mutations could be produced by means of X-rays. This suggested to his contemporaries the use of other agencies for this purpose. Since his announcement, other agencies that have experimentally been proved to produce a positive effect are, in their chronological order: beta and gamma radiation and ultra-violet light. In the production of mutations by X-rays, Muller, in 1927, showed that a heavy treatment caused a rise of approximately fifteen thousand percent in the mutation rate over that in the untreated cells. The effects of radium in producing mutations was shown by Hanson and Heys in 1928. They found that when adult flies were treated six hours with 140 milligrams of radium the percentage of lethal mutations produced was 8.2. When the beta rays were absorbed by a lead screen the gamma rays produced 2.8 percent of lethal mutations. The alpha-rays were absorbed by the walls of the needles which contained the source of radium. In 1928 Stadler found three mutations in radium-radiated barley seedlings out of 1,039 head progeny that he examined. In 1933 Altenburg succeeded in producing lethal mutations in Drosophila by irradiating eggs with u1tra-violet light. He reported the production of eight lethal mutations in 108 treated males, and showed that these mutations must have occurred during an interval of less than an hour at the time of raying. Since the occurrence of such a large percentage of lethals naturally in this short interval is highly improbable, the effect of ultra-violet light was definitely established. When I began working on this problem in 1932, no results had been published concerning the effects of alpha-radiation on Drosophila. Since then, Hanson published, in December of 1933, a note reporting that he had produced somatic variations and mosaics by means of alpha-radiation. I thought it would be of interest to investigate the genetic effects of alpha-radiation, and particularly whether germinal mutations could be produced. An important property of alpha-radiation, which is not common to any of the other types of radiation tested above, is that the ionization is not uniform but is concentrated along the extremely narrow paths of the alpha-particles; and along these paths the ionization is extremely intense. On this account it seemed that some interesting results might be obtained with alpha-rays which do not occur with the other types of radiation.