On the genetic background of the adaptive response to X-rays in Drosophila melanogaster

The effects of a low dose (0.1-20 mGy) preirradiation with X-rays followed by a higher dose (2 Gy) of the same radiation on the recovery of the genetic damage induced as dominant lethals in mature oocytes (stage 14) of different strains of Drosophila melanogaster were investigated. The response was shown to be dependent on the genotype of the flies tested, since lower frequencies of dominant lethals (DL) were only obtained in strains carrying the white mutation. Based on these observations experiments to locate the genetic factor responsible for the adaptive response (AR) were performed. This factor was found to be in a specific region of the X-chromosome. Additional experiments were carried out to give information on the minimal dose required to induce the AR. The results showed that the lowest dose needed is 0.2 mGy. Increasing the conditioning X-ray dose had no influence on the response.