What Is the Evolutionary Basis of Sex Determination Variability in Fish?

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What Is the Evolutionary Basis of Sex Determination Variability in Fish?

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Why is sex determination so diverse in fish compared to mammals and birds? It has been suggested that fish might have some developmental and genomic predisposing peculiarities, including a flexibility of differentiation of male and female gonads from a same precursor tissue, as well as a high number of gene duplicates and an important genomic plasticity [Volff, 2005; Froschauer et al., 2006; Mank et al., 2006]. However, the most important but so far largely unanswered question concerns the selection pressures behind the diversity of sex determination. Does the frequent switching between sex-determining systems provide any advantage to fish, or is it only a consequence of a peculiar mode of evolution? Particularly interesting is the fact that most Y and W sex chromosomes are poorly or not degenerate in fish despite an apparent suppression of recombination in the sex-determining region. Are fish sex chromosomes so poorly differentiated because they did not have time to degenerate, or bec

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