Meiosis is essential for eukaryotic sexual reproduction, and meiotic recombination redistributes genetic variations among progeny. Homologous recombination is also important for DNA repair and genome stability. Current recombination models include DNA synthesis, particularly leading-strand synthesis, but its role has not been tested experimentally. Here, we showed that mutations in a DNA polymerase required for leading-strand elongation caused reduced fertility, defects in meiotic chromosome fragmentation and segregation, and reduction of interference-sensitive cross-overs (COs). Because the majority of meiotic COs are produced from the interference-sensitive pathway in budding yeast, mammals, and flowering plants, the discovery of leading-strand elongation in the differentiation of meiotic recombination pathways has important implications in understanding of human reproductive health and crop breeding.