Investigations on radiosensitive and radioresistant populations of Drosophila melanogaster. VIII. The system of relative radioresistance in immature oocytes of the irradiated population ROI4.

Prophase I oocytes of the irradiated population ROI4 of Drosophila melanogaster are radioresistant relative to those of a control population (+K). The system of relative radioresistance is apparently dose-modifying and can be described by Dose-Reduction Factors (DRFs). At least 3 constituent components of the system can be distinguished, as follows. The genetic factor rar-1 contributes to the system with respect to the induction of dominant (DRF = 1.31) and sex-linked recessive lethals (DRF = 1.31) in a way that is inhibited by caffeine. The factor rar-2, independently reduces both types of lethal to the same amount as does rar-1, but also affects the production of X-chromosome loss (DFR = 1.72). The results of several different approaches allow, as a working hypothesis, the interpretation that rar-2 reduces the association of heterologous, chiasmatic chromosomes in the chromocentre in time and/or space and thus minimizes the preconditions for the production of certain types of interchange and of non-disjunction. A third factor, rar-3, is postulated to contribute, independently from the others, to the system of relative radioresistance with respect to dominant lethals (DRF = 1.58), interchanges and non-disjunction (DRFs = 1.58), and sex-linked recessive lethals (DRF = 1.87).