Sex Chromosome Turnover and Structural Genome Divergence Shapes Meiotic Outcomes in Hybridising Cobitis

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.