A study of induced somatic recombination in Drosophila melanogaster heterozygotes for autosome translocations: Estimation of the role of eu- and heterochromatin

The frequency of X-ray induced (1500 R) somatic recombination in the 2R-arm was studied in Drosophila melanogaster females heterozygous for translocations T(2;3) with break-points in different regions of chromosome 2, and in the control (without translocations). Heterozygosity for the brown mutations was used for recombination monitoring. In the system used, mainly exchanges in the '2R-break-point-brown' region lead to phenotypically discernible results, which permits estimation of the role of different 2R-arm regions in somatic recombination. It has been shown that translocations with break-point in the 2L-euchromatin had no effect on the frequency of somatic crossing over, while all translocations with break-point in 2R-euchromatin reduced it significantly. As for translocations with break-point in the centromere heterochromatin of chromosome 2, one of those had no effect on the recombination frequency and two others reduced it, though not to the extent characteristic of those with euchromatic break-points. Data obtained reveal that about 70% of the exchange events in the 2R-arm occur in the centromere heterochromatin. It is suggested that relative differences in somatic recombination frequencies in Drosophila eu- and heterochromatin can be due to different role of eu- and heterochromatic regions in somatic pairing of chromosomes.