Sex Chromosome Turnover and Structural Genome Divergence Shapes Meiotic Outcomes in Hybridising <i>Cobitis</i>

Our results demonstrate that individual orthologous chromosomes differ markedly in their ability to form bivalents during meiosis in hybrids, indicating that hybrid meiotic behaviour is shaped by chromosome-specific incompatibilities rather than uniform genome-wide failure. We also found that even closely related parental species possess distinct, non-homologous sex chromosomes, highlighting rapid turnover of sex determination systems in hybridising lineages. Together, these findings provide a high-resolution genomic and cytogenetic framework to explore how the architecture of inherited parental genomes influences sex-specific reproductive outcomes in hybrids-ranging from male sterility to the establishment of fertile, clonally reproducing female lineages-and how such asymmetries may contribute to the emergence of asexuality in vertebrates.