RADIATION DAMAGE IN THE DEVELOPING GERM CELLS OF Drosophila Virilis

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Abstract
The relationship between X-ray dosage and genetic damage was determined throughout the meiotic cycle. Damage was measured as dominant lethals and translocate cms. The number of aberrations varies from 20-100 fold between stages, depending on the physiological conditions at irradiation. The period (E) just after meiosis is the most susceptible of the stages. The early stages of the maturation of the sperm (E, D, and C) are the periods of differentiation of this unique cell type. Along with the complex changes in the cytoplasm during this period, there occurs the replacement of the histone protein by protamine protein in the chromosomes. The susceptibility of these stages is markedly influenced by modifications in the environment, such as increased amount of O2 or the presence of CO during irradiation. During the susceptible period especially (stages A, C, D, and E), the amount of X-ray damage measured as translocations is directly proportional to dosage above 300 r. Very few translocations are produced in pre-meiotic stages, although many dominant lethals occur. The late spermatogonia (stage G) are so susceptible to radiation injury that many cells in this stage die and few sperm are produced. Radiation damage to the different stages of oogenesis in the female Drosophila has been shown to be similar to that in Sciara and Habrobracon. The comparable stages in the male, stages H through F, respond to radiation very much as the female. Stages equivalent to stages E through A and mature sperm are not present in the female. The enzyme activity as modified by the gaseous environment influenced the amount of damage to pupae. Even without an external source of O2, irradiation in CO modified the internal environment and increased radiation damage above that in N2 at all stages. The sensitive stages of the maturation cycle in the male Drosophila are particularly useful in studying the relation between physiological activity and genetic damage from radiations.