Two genes required for meiotic recombination in Drosophila are expressed from a dicistronic message.

We have isolated two alleles of a previously unidentified meiotic recombination gene, mei-217. Genetic analysis of these mutants shows that mei-217 is a typical "precondition" gene. The phenotypes of the mutants are meiosis specific. The strongest allele has <10% of the normal level of crossing over, and the residual events are distributed abnormally. We have used double mutant analysis to position mei-217 in the meiotic recombination pathway. In general, mutations causing defects in the initiation of meiotic recombination are epistatic to mutations in mei-41 and spnB. These two mutations, however, are epistatic to mei-217, suggesting that recombination is initiated normally in mei-217 mutants. It is likely that mei-217 mutants are able to make Holliday junction intermediates but are defective in the production of crossovers. These phenotypes are most similar to mutants of the mei-218 gene. This is striking because mei-217 and mei-218 are part of the same transcription unit and are most likely produced from a dicistronic message.