Chromosomal recombination suppressors (RS) were induced and studied as part of a programme to induce and isolate temperature-sensitive recessive lethal factors, for subsequent use in genetic sexing mechanisms in the medfly, Ceratitis capitata (Wied.).
The presence of induced RS factors was identified through the complete linkage of two morphological markers, ap and dc, located 18.25 recombination units apart. Adult +dc males were irradiated one day after emergence with 50 Gy in a cobalt-60 source. The irradiated males were mated to marked ap + females and the F1 females were crossed to ap dc males. A total of 5 heterozygous RS factors was isolated from 570 irradiated and screened chromosomes. Suppression of female recombination in the heterozygous lines ranged from 77.6ยฐ7o in RS 19 to 99Aยฐ70 in RS 30B. Chromosomal analysis showed all RS lines to contain a single reciprocal translocation involving in all cases chromosome 3 and one other autosome. It appears that recombination between the two morphological markers is suppressed either through lethality conferred upon the gametes, which results from recombinant events taking place in the interstitial segment between the centromere and the translocation breakpoints, or through interference by the translocation heterozygote with the initiation or maintenance of cross-over synapsis thus preventing the appearance of cross-over products.
All 5 translocations involved chromosome 3 and one of the other autosomes, providing the first evidence for a correlation between the ap-dc linkage group and chromosome 3.