HIGH GENETIC INSTABILITY OF HETEROCHROMATIN AFTER TRANSPOSITION OF THE LINE-LIKE-I FACTOR IN DROSOPHILA-MELANOGASTER

In the present work, we have asked whether a group of 13 essential gen es mapping to the heterochromatin of Drosophila melanogaster chromosom e 2 are mutable following transposition of the I factor during I-R hyb rid dysgenesis. We found that the frequency of lethal events mapping t o chromosome 2 heterochromatin is surprisingly high, despite the low d ensity of genetic functions identified in this region compared with eu chromatin. Cytogenetic and molecular analyses indicated that the recov ered mutations correspond either to insertions or to rearrangements, M oreover, chromosomes bearing specific heterochromatic lethal mutations were generated by recombination in the heterochromatin, Together, the se data indicate that I factors transpose with high frequency into per icentric regions of chromosome 2 and may play a role in the evolution of constitutive heterochromatin.