Functional Divergence between the Z and W Alleles of the UBAP2 Gene Revealed by Differences in Their Expression Patterns in Japanese Quail

These findings indicate that UBAP2W has a distinct female-specific functional role in avian gonadal differentiation. We propose that UBAP2W contributes to ovarian development and oogenesis through the ubiquitin-proteasome pathway, while UBAP2Z is involved in general cellular regulation across sexes. This study highlights functional divergence between Z- and W-linked paralogs in birds and provides new insights into sex chromosome evolution and gonadal development.