While the interchromosomal effect (IC effect) has been well characterized at the phenotypic level, almost nothing is known about the mechanism. Crossovers that occur during meiosis require a specific set of proteins to form and are subject to crossover control mechanisms such as interference (these are the so-called Class I COs). However, COs can also form using mitotic-like CO pathways, but these use a different set of proteins and are not subject to crossover control mechanisms. I will be determining if the extra COs that form during the IC effect are Class I meiotic COs or the mitotic-like COs. To do this, I’ll measure the IC effect in mei-9 mutants and blm mutants. Evidence suggests that mei9 is playing a critical role in resolving recombination intermediates into COs during meiotic recombination by cleaving double Holiday junctions into COs. Therefore, the mei9 mutant would not be able to produce class I crossover. By comparing the CO distribution of mei9 mutant and mei9; +/TM6B, the identity of extra crossovers from IC effect can be determined. Blm mutant would produce crossovers that lack chromosomal interference, so those crossovers found in blm mutants are considered to be class II crossovers. Therefore, if the blm mutants with balancer are scored, I can further insight about those extra crossovers from IC effect.