CNTD1 (cyclin N-terminal domain containing 1) is a critical regulator of meiotic crossover formation and maturation. During meiosis, CNTD1 localizes to maturing crossover sites, where it colocalizes with other CO-specific factors including RNF212, HEI10, and MLH1 1. CNTD1 facilitates crossover differentiation through interaction with PRR19 and stimulates CO formation via interactions with RFC3 and RFC4, while simultaneously regulating cell-cycle progression through CDC34-mediated ubiquitination of WEE1. Additionally, CNTD1 participates in deselection of excess pre-CO intermediates [UniProt annotation]. The protein functions in the unloading of RNF212B at pachynema completion, demonstrating functional interplay with other E3 ligases essential for CO homeostasis 1. Loss of CNTD1 function severely impairs meiotic crossover formation, as demonstrated in zebrafish models where cntd1 knockout resulted in defective meiotic crossover formation, cell-cycle arrest at metaphase I, and production of unreduced gametes 2. In females, this leads to ploidy alterations and generation of polyploid offspring, providing direct evidence that CNTD1-dependent crossover defects are fundamental to polyploidization processes in vertebrates. These findings underscore CNTD1's essential role in ensuring accurate meiotic recombination and proper chromosome 17.