Meiosis is a fundamental process by which diploid organisms generate haploid gametes. Central to successful completion of meiosis is the formation of crossovers (COs) between DNA molecules of homologous chromosomes. CO events result in chiasmata, the physical links that hold chromosomes together and ensure proper segregation at the meiosis I division. Most organisms make very few COs per chromosome pair, indicating the process must be tightly regulated. The mechanism must ensure that each pair will undergo at least one CO, and at the same time, the formation of a CO will inhibit other COs nearby. COs are generated by homologous recombination initiated by DNA double strand breaks (DSBs) formed by the meiotic topoisomerease-like SPO-11 protein. There are more DSBs formed than COs, indicating that a subset of recombination precursors enter a CO pathway while the rest are repaired to give noncrossover (NCO) products. Despite the importance of crossing over for ensuring chromosome inheritance, the mechanisms that convert DSBs into COs and that regulate crossing over remain poorly understood. The goal of my project is to investigate the mechanism and regulation of meiotic recombination by analyzing recombination events at a defined locus. As an assay system, I am using worms heterozygous for two different alleles of the unc-5 gene, one of which contains a Mos1 transposon insertion. Induction of transposase causes transposon excision, thus forming a DSB that can lead to recombination. Intragenic recombination events at the unc-5 locus are identified by restoration of WT movement. Further, the CO vs. NCO status of the recovered recombinants is assessed using closely linked flanking markers. This will allow me to determine at what time point in meiosis DSBs are most likely to be converted into CO products and if a CO at this spot will cause interference. Furthermore, I will perform experiments in a spo11 background, which lacks the ability to initiate endogenous meiotic DSBs. In this context the transposon-excision break should be the only site of COs, which will occur on only one chromosome pair. This will allow the opportunity to test the relationship between the CO site and cytological markers of the emerging chiasma, to assess chromosome-wide changes initiated by the CO, and to evaluate the timing of how DSBs are processed into COs. Finally, I will perform these experiments in strains carrying mutations affecting other meiotic components to test how each component affects the outcome of the transposon-induced DSB.