Xie S, Li J, Chen W, Fong LJM, Huang C, Feng Y, Ai Q, Zhao M, Mank JE, Wu H.

Genome Res. 2025 Jun 2;35(6):1325-1336. doi:10.1101/gr.280161.124

Extreme heterochiasmy and high rates of sex-reversed recombination result in large yet homomorphic sex chromosomes in the Emei moustache toad.

“Population genetic data showed high rates of sex-reversed XY-type females, and recombination between the X and Y Chromosomes in these individuals helps maintain the integrity of sequence and gene expression on the Y Chromosome.” “Despite this large size and the assumption that inversions catalyze recombination suppression between the X and Y Chromosomes, we found little evidence of XY structural variation.” “High collinearity and similarity between X and Y haplotypes implicate a pre-existing pattern of low recombination itself, likely predating the origin of Chr 1 as the sex chromosomes, rather than structural variation, in sex chromosome formation.”