Hybrid dysgenesis in Drosophila melanogaster. I. Further evidence for and characterization of the mutator effect of the inducer-reactive interaction.

1. Several experiments were carried out to study, in the I-R hybrid dysgenesis system, the induction of recessive sex-linked lethal mutations in the progeny of SF females (obtained from crosses of female R by male I) or of RSF females (obtained from crosses of female I by male R). 2. Induced lethals were found in the progenies of SF females but not in those of RSF females. 3. The frequency of induced lethals decreased as SF females grew older. 4. A difference in the frequency of the induced lethals according to the reactive or inducer chromosome origin seemed apparent. Such frequency systematically appeared to be higher for the chromosomes of reactive origin. 5. The correlation between the rate of induced lethals and the intensity of the I-R interaction, as well as the characteristics of the lethals obtained and their non-random distribution, are in agreement with the hypothesis that the mutations are the consequence of the transposition of the I factor.