Male recombination is not induced in Drosophila melanogaster by extracts of strains with male recombination potential

Abstract

NON-TRIVIAL frequencies of spontaneous male recombination in the hybrid progeny of Drosophila melanogaster males from so-called ‘male recombination strains’ and laboratory marker stock females are well documented^1,2. Attempts to induce male recombination by injection have produced conflicting results. The positive results originally claimed by Reddi et al.³ were not reproducible in two subsequent studies^4,5. Sochacka and Woodruff⁶ have suggested that the disparity in results may be attributable to the use of extracts from a male recombination strain in the former study only. They injected extracts from the male recombination strain OK1 (ref. 7) into laboratory marker strain females. These were crossed to the Canton-S strain, which lacks spontaneous male recombination potential, producing F₁ hybrids which yielded a low frequency of male recombination. Injection directly into F₁ hybrid males also yielded some recombinants. Similar tests using Canton-S as the source of the extract were negative. We describe here large-scale tests with different male recombination strains. We could not reproduce the injection effect of Sochacka and Woodruff, suggesting that their results may not be generally applicable. We suggest, furthermore, that the genetic implications of a negative injection result may be at least as interesting as those of a positive result. A positive result would imply the existence of some co-existing, possibly non-essential, factor, such as a virus or episome. This would rule out explanations for male recombination based on incompatability of genetic organisation in different strains. Explanations of this type, for example, in terms of spatial organisation of chromosomes⁸, have potentially important implications for normal nuclear organisation.