Gene conversion in the shibirets locus of Drosophila melanogaster.

Abstract

Backcrossing heteroallelic shibirets (shits: 1 - ca 52) Drosophila melanogaster to either the shits1 or shits2 parent strain yields, with low frequency, recombinant progeny with shi+ phenotype. Such flies are easily selected, because in contrast to shits flies, they retain mobility and viability at 30oC at all stages of the life cycle. We examined progenies that potentially would have given approximately 4–105 shits flies, had the entire developmental periods transpired at the permissive temperature of 20oC. We assume that the 9 shi+ flies found did not arise by mutation. Eight of the 9 were heterozygous females and one was a male; 6 were gene convertants without exchange of outside markers. Of the 3 shi+ flies with changes in flanking marker combinations, at least one also was a convertant. Thus, if reciprocal crossing-over between the shits alleles with the expected outside marker exchange occurred at all, it was less than one fourth as frequent as conversion of shits to shi+. A priori we had hoped that the heteroallelic shits system, with strong selection for shi+ progeny, might be applicable to testing compounds for recombinogenic activity. Ethyl methanesulfonate, a known powerful recombinogen in yeast, did not enhance gene conversion reproducibly.