Evans Ben J.

No Thumbnail Available
Last Name
Evans
First Name
Ben J.
ORCID

Filters

2020 - 2023 2
2
2
Reset filters

Settings

Search Results

Now showing 1 - 2 of 2
  • Article
    A frog with three sex chromosomes that co-mingle together in nature: Xenopus tropicalis has a degenerate W and a Y that evolved from a Z chromosome
    (Public Library of Science, 2020-11-09) Furman, Benjamin L. S. ; Cauret, Caroline M. S. ; Knytl, Martin ; Song, Xue-Ying ; Premachandra, Tharindu ; Ofori-Boateng, Caleb ; Jordan, Danielle C. ; Horb, Marko E. ; Evans, Ben J.
    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 other Xenopus species, which suggests that sex differences in recombination are genus-wide. These findings are consistent with theoretical expectations associated with recombination suppression on sex chromosomes, demonstrate that several characteristics of old and established sex chromosomes (e.g., nucleotide divergence, sex biased expression) can arise well before sex chromosomes become cytogenetically distinguished, and show how these characteristics can have lingering consequences that are carried forward through sex chromosome turnovers.
  • Article
    Functional dissection and assembly of a small, newly evolved, W chromosome-specific genomic region of the African clawed frog Xenopus laevis
    (Public Library of Science, 2023-10-08) Cauret, Caroline M. S. ; Jordan, Danielle C. ; Kukoly, Lindsey M. ; Burton, Sarah R. ; Anele, Emmanuela U. ; Kwiecien, Jacek M. ; Gansauge, Marie-Theres ; Senthillmohan, Sinthu ; Greenbaum, Eli ; Meyer, Matthias ; Horb, Marko E. ; Evans, Ben J.
    Genetic triggers for sex determination are frequently co-inherited with other linked genes that may also influence one or more sex-specific phenotypes. To better understand how sex-limited regions evolve and function, we studied a small W chromosome-specific region of the frog Xenopus laevis that contains only three genes (dm-w, scan-w, ccdc69-w) and that drives female differentiation. Using gene editing, we found that the sex-determining function of this region requires dm-w but that scan-w and ccdc69-w are not essential for viability, female development, or fertility. Analysis of mesonephros+gonad transcriptomes during sexual differentiation illustrates masculinization of the dm-w knockout transcriptome, and identifies mostly non-overlapping sets of differentially expressed genes in separate knockout lines for each of these three W-specific gene compared to wildtype sisters. Capture sequencing of almost all Xenopus species and PCR surveys indicate that the female-determining function of dm-w is present in only a subset of species that carry this gene. These findings map out a dynamic evolutionary history of a newly evolved W chromosome-specific genomic region, whose components have distinctive functions that frequently degraded during Xenopus diversification, and evidence the evolutionary consequences of recombination suppression.