RADIATION-INDUCED LOSS OF RING-X CHROMOSOMES IN GERM CELLS OF DROSOPHILA MELANOGASTER MALES

A comparison was made between teh sensitivities of spermatocytes and postmeiotic germ cells, for the induction of XO males and sex-ratio shift. Adult males were irradiated and the treated germ cells were samples in a brooding scheme. In post-meiotic germ cells there was a uniform sensitivity for the induction of XO males. Within the range of exposured given, teh frequencies of XO males increased linearly with increasing exposure. In spermatocytes, which were themost sensitive germ-cell stage for the induction of XO males, the frequencies of XO males increased nonlinearly with increasing exposure. Significant sex-ratio shifts were found only when germ cells were samples on the first six days after irradiation. It was not possible to establishe a common relationship between the inductino of XO males and sec-ratio shift when post-meiotic germ cells were irradated. The highest frequenceis of XO males were found in the progeny from sperm samples on the eight day after irradiation. This was also the period when the fertlity of the irradiated males was most reduced. It is suggested that induced crossing-over may be the mechanism which is largely responsible for the production of high frequencies of XO males when spermatocytes are irradiated. © 1966.