Meiosis is the keystone of reproductive success in sexually reproductive organisms as failure to successfully complete meiosis results in aneuploidy, a leading cause of developmental diseases and miscarriages. Successful chromosome segregation is facilitated by using DNA recombination to form crossovers (COs) between homologous chromosomes. Not all recombination events result in a CO however and the majority are repaired as noncrossovers (NCOs). Thus, the decision whether to form a CO or NCO is a critical regulatory point during meiosis that is poorly understood. Despite having a clear picture of the genetic requirements for a crossover to form, it is completely unknown why some breaks are chosen to be repaired as crossovers and others as noncrossovers. The parent grant of the current equipment supplement addresses this critical knowledge gap by using heterozygous chromosome inversions in Drosophila melanogaster as a model. Heterozygous inversions pose an interesting problem for the meiotic program. Meiosis requires that homologous chromosomes recognize and use each other as templates for precise repair during recombination, yet inversions disrupt the synteny between homologs. There are two downstream effects: COs are suppressed locally on the inversion chromosome, and a checkpoint is activated, which leads to a genome-wide increase in COs on non-inverted chromosomes. We have shown that these responses are mediated through changing the CO vs. NCO decision. In this equipment supplement, we are requesting funds to purchase the Imaris image analysis software from Oxford Instruments. We currently have the microscopes we need (including a Leica Stellaris 5 confocal owned by us and housed in our lab, and access to a Leica TCS SP8 gated STED microscope housed in the CWRU Light Microscopy Core), but we do not have access to Imaris. Along with the purchase of the software, we are also requesting funds for 3 years of the maintenance plan that will include unlimited technical training and support for applications specific to our use case. Purchase of this software will generate data critical for analyzing the structure of the synaptonemal complex at inversion breakpoints and insight into defects in the structure that alter the CO/NCO decision, a high- priority goal of the parent grant. Importantly, the methods we are proposing have been successfully carried out by other Drosophila meiosis labs multiple times; we will be applying those methods to our own system.