Preprint identifies achiasmatic meiosis as mechanism enabling clonal genome propagation in hybrid crucian carp females

A preprint posted to bioRxiv on 3 June 2026 investigates the cellular basis of asexual reproduction in *Carassius gibelio* (the Prussian carp or silver crucian carp), a hexaploid hybrid fish complex in which females reproduce largely clonally — meaning offspring are genetically near-identical to the mother — whilst males of co-occurring sexual tetraploid lineages provide sperm that activate but do not genetically contribute to development.

The authors characterised meiotic progression and gametogenesis in both the asexual hexaploid females and sexual tetraploid conspecifics. In asexual females, they find that meiosis proceeds without the formation of chiasmata — the physical crossover structures between homologous chromosomes that normally generate genetic diversity and are essential for accurate chromosome segregation in canonical meiosis. This achiasmatic meiosis allows females to produce unreduced (diploid rather than haploid) eggs that preserve the full clonal genome, avoiding the genetic reshuffling that would otherwise disrupt clonal inheritance.

Additionally, the authors document that the same achiasmatic mechanism facilitates reliable transmission of supernumerary B chromosomes — selfish genetic elements that are not part of the standard karyotype — to offspring in asexual but not sexual lineages.

The work contributes to understanding how transitions from sexual to asexual reproduction are mechanistically achieved in vertebrates, a question with broader relevance to evolutionary genetics and reproductive biology. **This is a preprint that has not yet undergone peer review.**