title: A large pseudoautosomal region on the sex chromosomes of the frog Silurana tropicalis.
abstract: Sex chromosome divergence has been documented across phylogenetically diverse species, with amphibians typically having cytologically nondiverged ("homomorphic") sex chromosomes. With an aim of further characterizing sex chromosome divergence of an amphibian, we used "RAD-tags" and Sanger sequencing to examine sex specificity and heterozygosity in the Western clawed frog Silurana tropicalis (also known as Xenopus tropicalis). Our findings based on approximately 20 million genotype calls and approximately 200 polymerase chain reaction-amplified regions across multiple male and female genomes failed to identify a substantially sized genomic region with genotypic hallmarks of sex chromosome divergence, including in regions known to be tightly linked to the sex-determining region. We also found that expression and molecular evolution of genes linked to the sex-determining region did not differ substantially from genes in other parts of the genome. This suggests that the pseudoautosomal region, where recombination occurs, comprises a large portion of the sex chromosomes of S. tropicalis. These results may in part explain why African clawed frogs have such a high incidence of polyploidization, shed light on why amphibians have a high rate of sex chromosome turnover, and raise questions about why homomorphic sex chromosomes are so prevalent in amphibians.
authors.affiliation: Department of Biology, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Bewick
authors.forename: Frédéric J J
authors.initials: FJ
authors.lastname: Chain
authors.forename: Lyle B
authors.initials: LB
authors.lastname: Zimmerman
authors.forename: Abdul
authors.initials: A
authors.lastname: Sesay
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Gilchrist
authors.forename: Nick D L
authors.initials: ND
authors.lastname: Owens
authors.forename: Eva
authors.initials: E
authors.lastname: Seifertova
authors.forename: Vladimir
authors.initials: V
authors.lastname: Krylov
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Macha
authors.forename: Tereza
authors.initials: T
authors.lastname: Tlapakova
authors.forename: Svatava
authors.initials: S
authors.lastname: Kubickova
authors.forename: Halina
authors.initials: H
authors.lastname: Cernohorska
authors.forename: Vojtech
authors.initials: V
authors.lastname: Zarsky
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Evans
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D005260:Female; D015870:Gene Expression; D005838:Genotype; D008297:Male; D012730:Sex Chromosomes / Q000235:genetics*; D014981:Xenopus / Q000235:genetics*
keywords: African clawed frogs; Xenopus tropicalis; pseudoautosomal region; recombination; sex chromosome; sex determination