PROJECT SUMMARY Recombination between chromosomes is required to generate genetic variation, maintain genome integrity, and ensure proper chromosome segregation during meiosis, the specialized cell division program that generates 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 programmed double strand DNA breaks (DSBs), which are repaired using meiosis-specific mechanisms that 1) favor utilization of the homologous chromosome (instead of the sister chromatid) as the repair partner; and, 2) promote a crossover outcome of the DSB repair process, which is required for proper chromosome segregation during meiosis. The goal of our research program is to understand how chromosomes are able to access distinct recombination pathways and partners to ensure faithful genome inheritance. Using in vivo assays we developed in the model system Caenorhabditis elegans, we have directly detected and analyzed use of the sister chromatid as a repair template during metazoan meiotic prophase I progression. Building upon our published work, we are defining and establishing how specific chromosome structures, proteins, and cellular contexts regulate recombination pathway and repair partner choices to maintain meiotic genome integrity. To expand and increase the both the accuracy and impact of the experiments of our research program, we are requesting with this administrative equipment supplement to obtain a droplet digital PCR system (ddPCR) for absolute quantification of DNA for our in vivo assays and our genomics datasets. Specifically, the requested instrument will enable: 1) absolute quantification of DSBs and DSB outcomes; 2) efficient detection and quantification of conversions tracts; 3) absolute quantification of single nucleotide polymorphisms (SNPs), copy number variations (CNVs), and mutations; and, 4) confirmation and validation of DSB outcomes across the genome within populations. Overall, the requested ddPCR system will enable us to expand and increase the accuracy and efficiency of our experiments that are determining the molecular signatures, chromosomal features, and proteins associated with DSB repair outcomes that are central to maintaining genomic integrity during sperm and egg development.