A Drosophila model of improving the fitness of translocations for genetic control : 1. Autosomal translocations with euchromatic breakpoints.

Translocations with euchromatic breakpoints were generated in lethal-free autosomes of Drosophila melanogaster. Pairs of initially homozygous-lethal translocations, matched for one breakpoint, were allowed to recombine for ten generations. At the end of the experiment, 10/47=21% of crosses (representing 8/26=31% of the intial translocations) had at least one line with at least one homokaryotypic third-instar larva, detected among a small sample of salivary gland preparations from each cross. Among these ten crosses, chromosome extractions were performed; 5/10 of the crosses (probably representing 4/8 of the translocations) had at least one chromosome set with relative viability greater than 15%-25%. To a first (and conservative) approximation, 5/47=11% of crosses showed improvement of viability of 1 of the translocations in the cross during the controlled recombination regime; overall, 4 of the 26 translocations (15%) showed improvement of viability. Partly because of the conservative criterion of viability used, this figure is less than the 20% of translocations that theoretically should be improvable. Pseudohomokaryotypes (pairs of translocations with both breakpoints nearly matching) did not behave as very fit homokaryotypes. However, some of them generated viable hyperploid assortment products that might be of practical interest to mask deleterious effects at breakpoints of translocations. The improvement of fitness of at least a proportion of low fitness translocation stocks by the use of a controlled recombination procedure should be feasible for many pest species.