[Cytogenetic analysis of the chromosomal region containing the radiosensitivity genes of Drosophila. Influence of pericentromeric heterochromatin on mutagenesis in the 44-45 region of chromosome 2].

Formation of radiation-induced mutations in the 44-45 region of Drosophila melanogaster chromosome 2 carrying the In(2)G50 inversion which juxtaposes the material of this region towards the centromeric heterochromatin was studied. 14 gamma-induced rearrangements in the inverted chromosome having a new breakpoint in the 44-45 region were selected. Four of them are deletions, seven are translocations and three are transpositions. 10 of these aberrations have a second breakpoint located in the heterochromatin regions of chromosomes 2 and 3. It was shown that the frequency of deletions in the region studied is tenfold higher within the inverted chromosomes as compared with the structurally normal one. Anyway, it is essentially lower than the frequency determined in analogous experiments for the other region of the chromosome. Thus, the peculiar characteristics of radiation mutagenesis in the 44-45 region, such as the prevalence of heterochromatic aberrations in the rearrangement spectrum and the relatively low deficiency frequency are still retained after inversional shift of this region to the pericentromeric heterochromatin.