Mapping the sex chromosomes of Silurana (Xenopus) tropicalis using RADseq. Xenopus tropicalis

Sex chromosomes have evolved from autosomes multiple times in plants and animals. Sex chromosome evolution theory predicts that suppression of recombination around a sex determining gene should spread to much of the chromosome. Over time suppressed recombination leads to divergence (referred to as degeneration) between the sex chromosomes. For example, the sex chromosomes of humans were once fully recombining homologous autosomes, but now the male-specific Y chromosome is minuscule compared to the shared X chromosome. Why is it then that sex chromosomes in some species do not degenerate even after substantial amounts of evolutionary time? We set out to better understand mechanisms that are potentially related to sex chromosome homomorphy by characterizing the sex chromosomes of the female heterogametic frog Silurana (Xenopus) tropicalis in terms of the size, divergence, and molecular evolution and expression of the sex-linked genes.