Research Summary Recombination between chromosomes is required to generate genetic variation, maintain genome integrity through the repair of double strand DNA breaks (DSBs), and ensure proper chromosome segregation during meiosis, the specialized cell division program by which diploid organisms generate haploid gametes such as sperm and eggs. Perturbations in recombination can compromise these basic cellular functions, ultimately leading to cancer, infertility, or birth defects. Meiotic recombination is initiated by DSBs, which are repaired using meiosis-specific mechanisms that favor utilization of the homologous chromosome (instead of the sister chromatid) as the recombination partner and that promote a crossover outcome of the DSB repair process, which is required for promoting proper chromosome segregation during meiosis. Although repair of DSBs with the appropriate template (homologous chromosome) is necessary for proper chromosome segregation and genome integrity, our knowledge about how germ cells achieve this template preference in the presence of nearly identical sequences (sister chromatids) is limited. Using Caenorhabditis elegans as a model system, we have developed a fluorescent assay to monitor repair of an induced DSB with the sister chromatid during meiotic prophase progression in vivo. One of the primary goals of the funded grant is to use this assay to determine how these different repair partner choices are regulated. To visualize the localization of proteins and markers associated with DSB repair and chromosome structures in both live and fixed germ cells and whole intact C. elegans, we utilize a widefield deconvolution microscope. Recently, the LED light source for this critical microscope suddenly became nonfunctional and requires replacement. All of our experiments associated with this grant are at standstill until the LED light source is replaced. This supplement will support the purchase of replacement LED light source that is required for function of the microscope. Overall, the requested light source replacement is essential for our research program and will enable us to achieve our goals to identify the molecular signatures, chromosomal features, and proteins associated with these different repair outcomes that are central to maintaining genomic integrity during sperm and egg development.