Differences in the induction of specific deletions and duplications by two male recombination factors isolated from the same Drosophila natural population.

2 male recombination factors, the 31.1 and 23.5 MRF isolated from the same natural population, were tested for the induction of specific deletions and duplications in the regions b and cn of the second chromosome. Genetic and cytological analysis of the double recombinants derived from appropriate crosses of the 23.5/CyL4 and 31.1/CyL4 strains with the dp b cn bw; ve revealed the following differences between the 2 MRFs. (1) The 23.5 MRF induced (a) higher frequencies of double "putative' recombinants, which often appeared in large clusters, (b) large clusters of single recombinants and (c) cases were the wild-type and sometimes the dp b cn bw phenotype were not produced among the F2-F10 progeny. Such cases were never found with 31.1 MRF. (2) The b and cn recombinants carried deletions whereas the reciprocal dp cn bw and dp b bw had duplications of the corresponding regions. Each cluster carried an identical deletion or duplication. (3) The breakpoints of the 22 cn deletions detected were distributed in the polytene region 42E-44C. On the basis of the cn deletions, we mapped the cn and so loci to polytene intervals 43E6-16 and 42E3.4--43C5.6, respectively. Hypotheses explaining the different results obtained by the 2 factors are discussed.