Outcross-dependent transpositions of copia-like mobile genetic elements in chromosomes of an inbred Drosophila melanogaster stock

Summary Transpositions of copia-like mobile genetic elements (MDG1, MDG3 and copia) were studied in crosses of the inbred maladaptive LA line with other laboratory lines made in order to replace specific chromosome pairs in the LA line. Individuals with various hybrid genotypes displayed changed chromosomal patterns of mobile elements compared with the parent LA chromosomes. Variability of the chromosomal molecular structure in hybrids was observed when crossing over was suppressed in the process of hybrid genome constructions. Multiple transposition events were detected in hybrid genomes carrying the second chromosomal pair of the LA line, but not if it was replaced by the second chromosome of the Swedish-b stock. No transpositions were detected in control crosses that did not involve the LA line. Outcross-dependent MDG1 transposition hot spots in the LA second chromosome were found to coincide with previously established hot spots for spontaneous transpositions in the LA line coupled with a fitness increase. The data obtained demonstrate that crosses involving inversions suppressing crossing over cannot guarantee that the chromosomal molecular content will remain the same: it can change as a result of mobile element trans-positions.