In mammalian meiosis, homologous chromosomes pair, synapse, and undergo genetic recombination, or the exchange of genetic material through crossing over. The appropriate frequency and distribution of crossovers is essential for ensuring equal segregation of homologs at the first meiotic division. Crossover formation is initiated by 250-300 DSBs of which 90% are resolved as non-crossovers, while 10% are resolved as crossovers. MLH1/MLH3 (MutLγ) contains a putative endonuclease domain in MLH3 thought to be essential for crossover formation. One focus of this thesis was to elucidate the role of MutLγ in crossover resolution in vivo, while investigating how MutLγ is recruited to chromosomes at the appropriate time and frequency. We generated an Mlh3D1185N mouse (Mlh3DN/DN) harboring a point mutation within the endonuclease domain. Mlh3DN/DN males are infertile, yet exhibit normal mating behavior. Mlh3DN/DN spermatocytes exhibit normal DSB formation, synapsis, and localization of MutLγ to chromosomes. However, Mlh3DN/DN pachytene spermatocytes exhibit persistence of RAD51 and BLM. Diakinesis-staged cells show reduced crossovers, but somewhat elevated above that of Mlh3-/- males. Thus, the MLH3 endonuclease domain is essential for processing of the majority of DSB events ultimately destined to become crossovers. CNTD1 is implicated in designating DSB repair intermediates to become crossovers in male meiosis; however, the meiotic phenotype of Cntd1GT/GT females is unknown. Thus, the second focus of this thesis was to elucidate CNTD1 function during prophase I in females. Cntd1GT/GT females are infertile, yet exhibit normal mating behavior. Initial DSB processing events are normal in Cntd1GT/GT oocytes, yet pachytene oocytes have a high rate of synapsis defects and fail to recruit MutLγ to chromosomes, leading to significantly fewer chiasmata compared to Cntd1+/+ oocytes. Cntd1GT/GT oocytes also show severe spindle defects and abnormal chromosome arrangement. Histologically, pre-pubertal Cntd1GT/GT ovaries have fewer follicles when compared to Cntd1+/+ ovaries, and are depleted of oocytes by adulthood. Thus, CNTD1 is not essential for early DSB processing events, but is required for MutLγ recruitment and Class I crossover designation. Crossover formation (MLH3) and designation (CNTD1) must be controlled temporally, spatially, and quantitatively. It is this fascinating and exquisitely complex regulation that forms the basis for the studies outlined in this thesis.