Radiation-induced translocations in inseminated eggs of Drosophila melanogaster

Abstract

The induction of reciprocal translocations by X-irradiation (500 R) of freshly laid inseminated eggs of Drosophila melanogaster was studied. In such eggs the maternal and paternal chromosome sets are exposed while they are within the same cell but in spatially separated nuclei. A constant rate of 0.3% translocations within the maternal chromosome set was found throughout the period during which the maternal genome passes from meiotic metaphase I to the pronuclear stage. During the same period the sperm head, containing the paternal chromosome set, transforms into the paternal pronucleus. At the beginning of this transformation a rate of 2.3% translocations within the paternal chromosome set was found. This rate fell, with the progression towards the pronuclear stage, to about 0.2%. From the recovery of three maternal-paternal translocations it was estimated that the maximal rejoining time of chromosome breaks was on the order of 10 min.