The Effects of γ-rays on Fecundity and Mutagenesis in Oregon-R Males of Drosophila

Abstract

Oregon-R males were tested in day-by-day sperm samples for dominant visible and hemizygous sex-linked mutations, fecundity (number of offspring produced), and crossing-over after exposure to cobalt-60 γ in the 100 r to 10 kr range. Tests totalled 42 184 X-chromosomes and 210 111 flies. Mutations were most frequent after irradiation during meiosis and spermiogenesis in low doses. Only sperm and gonial cells subsequently produced adult flies after exposure to 5 kr and 10 kr. After 500 r fecundity was reduced chiefly in cells in late mitosis, and in earlier and later stages with increasing doses. Reduced fecundity may not be due to the kind of mutation detected here, but both effects may combine to influence the frequency of mutations recovered, particularly from irradiated meiotic and spermiogenic cells. Males receiving 500 r might contribute more mutations to a population's gene pool than competing males after a substantially higher dose.