Time of recombination in the Drosophila melanogaster oocyte. II. Electron microscopic and genetic studies of a temperature-sensitive recombination mutant.

A test has been carried out to determine if the restrictive temperature (31 degrees) acts to reduce recombination in the temperature-sensitive recombination-deficient genotype rec-l26/rec-l16 by reducing or eliminating the synaptonemal complex. Measurements of the length of synaptonemal complexes in heat-treated and untreated stage 1 oocytes, following termination of the temperature-sensitive period, reveal less than a 5% difference, with the greater length present in the treated oocytes. Alterations are not observed in synaptonemal complex distribution within the nucleus or in its fine structure. Parallel genetic studies confirm earlier observations that the restrictive temperature, whose action is confined to a 36-h sensitive period virtually coextensive with premeiotic-S, drastically reduces recombination to approximately 10% of normal. The results are most simply interpreted to mean that the restrictive temperatures acts directly on the recombination process.