Reply to Wright et al.: How to explain the absence of extensive Y-specific regions in the guppy sex chromosomes

Wright et al. (1) are correct that our genomic data for the guppy sex chromosome are not dissimilar from theirs. However, our conclusion truly differs from their previous chief conclusion that “evolutionary strata” are evolving (2). Strata are sex chromosome regions that evolved suppressed recombination in separate events, each establishing a nonrecombining region, isolating Y-linked sequences from their X-linked alleles for substantial evolutionary times and creating physical regions of an X/Y or Z/W sex chromosome pair with different divergence. Sequence divergence suggests that the most recent recombination suppression event in humans occurred at least 30 million years ago (3, 4), and more recently in plant sex chromosomes (5⇓–7). In contrast, both guppy genomic datasets (2, 8) are compatible … [↵][1]1To whom correspondence may be addressed. Email: r.bergero{at}ed.ac.uk. [1]: #xref-corresp-1-1