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The Diversity and Evolution of Sex Chromosomes in Frogs
Ma, Wen-Juan Veltsos, Paris
Ma, Wen-Juan
Veltsos, Paris
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Abstract
Frogs are ideal organisms for studying sex chromosome evolution because of their diversity in sex chromosome differentiation and sex-determination systems. We review 222 anuran frogs, spanning ~220 Myr of divergence, with characterized sex chromosomes, and discuss their evolution, phylogenetic distribution and transitions between homomorphic and heteromorphic states, as well as between sex-determination systems. Most (~75%) anurans have homomorphic sex chromosomes, with XY systems being three times more common than ZW systems. Most remaining anurans (~25%) have heteromorphic sex chromosomes, with XY and ZW systems almost equally represented. There are Y-autosome fusions in 11 species, and no W-/Z-/X-autosome fusions are known. The phylogeny represents at least 19 transitions between sex-determination systems and at least 16 cases of independent evolution of heteromorphic sex chromosomes from homomorphy, the likely ancestral state. Five lineages mostly have heteromorphic sex chromosomes, which might have evolved due to demographic and sexual selection attributes of those lineages. Males do not recombine over most of their genome, regardless of which is the heterogametic sex. Nevertheless, telomere-restricted recombination between ZW chromosomes has evolved at least once. More comparative genomic studies are needed to understand the evolutionary trajectories of sex chromosomes among frog lineages, especially in the ZW systems.
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Date
2021-03-26
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MDPI
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Keywords
Anurans, Sex chromosome diversity, Homomorphy, Heteromorphy, Sex determination, Fountain of youth, Sexually antagonistic selection, Sex-determination turnover, Telomere-restricted recombination
Citation
Ma, W.-J.; Veltsos, P. The Diversity and Evolution of Sex Chromosomes in Frogs. Genes 2021, 12, 483. https://doi.org/10.3390/genes12040483