Meiotic Recombination in Teleosts.

Teleosts (teleost fishes), comprising over 30,000 species-roughly half of all living vertebrates-exhibit remarkably diverse patterns of meiotic recombination. Recent genome-wide analyses as well as cytological studies provide new insights built on decades of genetic research. In most teleosts, crossovers are concentrated near chromosome ends, producing strong heterochiasmy largely driven by male meiosis. Despite sharing conserved recombination machinery with mammals, teleosts show strikingly relaxed meiotic checkpoints, allowing meiotic progression and gamete formation even with severe recombination defects. This tolerance likely facilitates hybridization, polyploidy, and clonal reproduction commonly observed in teleosts. The recombination hotspot regulator PRDM9 has diversified dramatically across teleost lineages: some retain the full-length Prdm9α that determines recombination hotspots, whereas most species possess only a truncated Prdm9β and likely rely on PRDM9-independent recombination. Cytological analyses further reveal dynamic synapsis and partial recombination suppression on emerging sex chromosomes. This review summarizes the current understanding of meiotic recombination in teleost fishes, integrating evidence from recombination landscape diversity, molecular pathways, cytological features, PRDM9 evolution, and distinctive phenomena such as sex chromosome differentiation, clonal reproduction, hybridization, polyploidy tolerance, and relaxed checkpoint control. Together, these findings illustrate how the remarkable lineage-specific adaptations of teleosts can serve as a powerful lens for revealing the fundamental significance of meiotic recombination across vertebrates.