A frog with three sex chromosomes that co-mingle together in nature: < i > Xenopus tropicalis < /i > has a degenerate W and a Y that evolved from a Z chromosome

by Benjamin L. S. Furman, Caroline M. S. Cauret, Martin Knytl, Xue-Ying Song, Tharindu Premachandra, Caleb Ofori-Boateng, Danielle C. Jordan, Marko E. Horb, Ben J. Evans In many species, sexual differentiation is a vital prelude to reproduction, and disruption of this process can have severe fitness effects, including sterility. It is thus interesting that genetic systems governing sexual differentiation vary among—and even within—species. To understand these systems more, we investigated a rare example of a frog with three sex chromosomes: the Western clawed frog,Xenopus tropicalis. We demonstrate that natural populations from the western and eastern edges of Ghana have a young Y chromosome, and that a male-determining factor on this Y chromosome is in a very similar genomic location as a previously known female-determining factor on the W chromosome. Nucleotide polymorphism of expressed transcripts suggests genetic degeneration on the W chromosome, emergence of a new Y chromosome from an ancestral Z chromosome, and natural co-mingling of the W, Z, and Y chromosomes in the same population. Compared to the rest of the genome, a small sex-associated portion of the sex chromosomes has a 50-fold enrichment of transcripts with male-biased expression during early gonadal differentiation. Additionally,X. tropicalis has sex-differences in the rates and genomic locations of recombination events during gametogenesis that are similar to at least two otherXenopus species, which sug...
Source: PLoS Genetics - Category: Genetics & Stem Cells Authors: Source Type: research