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The stickleback system offers a powerful model for investigating the evolutionary dynamics of sex chromosome differentiation. Although a ZW sex determination mechanism has previously been reported in sticklebacks, its origin and evolutionary history remain poorly resolved. Here, integrated multiomics analyses were applied to elucidate the evolutionary trajectory of the ZW system in Pungitius sinensis and Pungitius bussei . Using two newly assembled genomes and family-based segregation data, the sex-determining region (SDR) was delineated with high resolution. Several canonical genes implicated in sex determination pathways were located within the identified SDR, although the primary sex-determining gene could not be definitively identified. Phylogenomic evidence indicated that the ZW system emerged in Pungitius sticklebacks at least 5.0 million years ago. The absence of strong selective pressure may account for the limited differentiation between Z and W chromosomes. These findings define the evolutionary framework of the ZW system in Pungitius and contribute to a broader understanding of the extensive sex chromosome diversity in teleosts.
Cheng et al. (Fri,) studied this question.