The kinetics of X-ray-induced somatic crossing-over in Drosophila melanogaster and the effects of dose fractionation

Protective effect of ethanol on X‐ray‐induced mitotic recombination in drosophila melanogaster

“…Yet the possibility that a less known action of ethanol also contributes to the effect observed should also be considered, particularly keeping in mind the complexities involved in X-ray-induced mitotic recombination. Several lines of evidence indicate that some mitotic recombination events are the result of two or more hits [Haendle, 1971b;Merriam and Fyffe, 1972;Becker, 19761. By varying the conditions of X-irradiation and using the w/wco twin spot system, Haendle [1971a,b] found that two different breakage-fusion mechanisms are involved in the induction of mitotic recombination. One mechanism is characterized by a fast repair system and the breaks restitute within 30 sec.…”

“…The second mechanism was found to be independent of time up to 150 sec, and the frequency of spots tended to decrease only when the time of irradiation lasted longer. Merriam and Fyffe [1972] found that the rejoining of X-ray-induced breaks is completed within 10 min and suggested that a general mechanism of repair may exist in Drosophila, because a similar repair time was observed in stage 7 oocytes [Parker and Hammond, 19581. As expected, a very low dose rate, and fractionation of the dose in four quarters separated by intervals of 80 min, led to a linear increase of twin spots in the wings [Ayaki et al, 19911. From the above-mentioned reports on the role played by repair in the induction of somatic recombination, it follows that no exchange will occur if a pair of broken ends in a chromosome restitute before they can interact with a second pair originated shortly after in its homologue.…”