Sex Chromosome

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Melissa J Perry - One of the best experts on this subject based on the ideXlab platform.

Judith E Mank - One of the best experts on this subject based on the ideXlab platform.

  • Sex Chromosome evolution so many exceptions to the rules
    Genome Biology and Evolution, 2020
    Co-Authors: Benjamin L S Furman, David C H Metzger, Iulia Darolti, Alison E Wright, Benjamin A Sandkam, Pedro Almeida, Jacelyn J Shu, Judith E Mank
    Abstract:

    Genomic analysis of many nonmodel species has uncovered an incredible diversity of Sex Chromosome systems, making it possible to empirically test the rich body of evolutionary theory that describes each stage of Sex Chromosome evolution. Classic theory predicts that Sex Chromosomes originate from a pair of homologous autosomes and recombination between them is suppressed via inversions to resolve Sexual conflict. The resulting degradation of the Y Chromosome gene content creates the need for dosage compensation in the heterogametic Sex. Sex Chromosome theory also implies a linear process, starting from Sex Chromosome origin and progressing to heteromorphism. Despite many convergent genomic patterns exhibited by independently evolved Sex Chromosome systems, and many case studies supporting these theoretical predictions, emerging data provide numerous interesting exceptions to these long-standing theories, and suggest that the remarkable diversity of Sex Chromosomes is matched by a similar diversity in their evolution. For example, it is clear that Sex Chromosome pairs are not always derived from homologous autosomes. In addition, both the cause and the mechanism of recombination suppression between Sex Chromosome pairs remain unclear, and it may be that the spread of recombination suppression is a more gradual process than previously thought. It is also clear that dosage compensation can be achieved in many ways, and displays a range of efficacy in different systems. Finally, the remarkable turnover of Sex Chromosomes in many systems, as well as variation in the rate of Sex Chromosome divergence, suggest that assumptions about the inevitable linearity of Sex Chromosome evolution are not always empirically supported, and the drivers of the birth-death cycle of Sex Chromosome evolution remain to be elucidated. Here, we concentrate on how the diversity in Sex Chromosomes across taxa highlights an equal diversity in each stage of Sex Chromosome evolution.

  • how to make a Sex Chromosome
    Nature Communications, 2016
    Co-Authors: Alison E Wright, Rebecca Dean, Fabian Zimmer, Judith E Mank
    Abstract:

    Sex Chromosomes can evolve once recombination is halted between a homologous pair of Chromosomes. Owing to detailed studies using key model systems, we have a nuanced understanding and a rich review literature of what happens to Sex Chromosomes once recombination is arrested. However, three broad questions remain unanswered. First, why do Sex Chromosomes stop recombining in the first place? Second, how is recombination halted? Finally, why does the spread of recombination suppression, and therefore the rate of Sex Chromosome divergence, vary so substantially across clades? In this review, we consider each of these three questions in turn to address fundamental questions in the field, summarize our current understanding, and highlight important areas for future work.

  • Sex Chromosome dosage compensation definitely not for everyone
    Trends in Genetics, 2013
    Co-Authors: Judith E Mank
    Abstract:

    Sex Chromosomes often entail gene dose differences between the Sexes, which if not compensated for, lead to differences between males and females in the expression of Sex-linked genes. Recent work has shown that different organisms respond to Sex Chromosome dose in a variety of ways, ranging from complete Sex Chromosome dosage compensation in some species to active compensation of only a minority genes in other organisms. Although we still do not understand the implications of the diversity in Sex Chromosome dosage compensation, its realization has created exciting new opportunities to study the evolution, mechanism, and consequences of gene regulation. However, confusion remains as to what sorts of genes are likely to be dosage compensated, how dosage compensation evolves, and why complete dosage compensation appears to be limited to male heterogametic species. In this review, I survey the status of dosage compensation to answer these questions and identify current controversies in this fast-moving field.

  • some inconvenient truths about Sex Chromosome dosage compensation and the potential role of Sexual conflict
    Evolution, 2011
    Co-Authors: Judith E Mank, David J Hosken, Nina Wedell
    Abstract:

    Sex Chromosome dosage compensation was once thought to be required to balance gene expression levels between Sex-linked and autosomal genes in the heterogametic Sex. Recent evidence from a range of animals has indicated that although Sex Chromosome dosage compensation exists in some clades, it is far from a necessary companion to Sex Chromosome evolution, and is in fact rather rare in animals. This raises questions about why complex dosage compensation mechanisms arise in some clades when they are not strictly needed, and suggests that the role of Sex-specific selection in Sex Chromosome gene regulation should be reassessed. We show there exists a tremendous diversity in the mechanisms that regulate gene dosage and argue that Sexual conflict may be an overlooked agent responsible for some of the variation seen in Sex Chromosome gene dose regulation.

Hans Ellegren - One of the best experts on this subject based on the ideXlab platform.

  • lack of dosage compensation accompanies the arrested stage of Sex Chromosome evolution in ostriches
    Molecular Biology and Evolution, 2013
    Co-Authors: Sofia Adolfsson, Hans Ellegren
    Abstract:

    Sex Chromosome evolution is usually seen as a process that, once initiated, will inevitably progress toward an advanced stage of degeneration of the nonrecombining Chromosome. However, despite evidence that avian Sex Chromosome evolution was initiated >100 Ma, ratite birds have been trapped in an arrested stage of Sex Chromosome divergence. We performed RNA sequencing of several tissues from male and female ostriches and assembled the transcriptome de novo. A total of 315 Z-linked genes fell into two categories: those that have equal expression level in the two Sexes (for which Z–W recombination still occurs) and those that have a 2-fold excess of male expression (for which Z–W recombination has ceased). We suggest that failure to evolve dosage compensation has constrained Sex Chromosome divergence in this basal avian lineage. Our results indicate that dosage compensation is a prerequisite for, not only a consequence of, Sex Chromosome evolution.

  • Sex-Chromosome evolution: recent progress and the influence of male and female heterogamety
    Nature Reviews Genetics, 2011
    Co-Authors: Hans Ellegren
    Abstract:

    Sex Chromosomes have raised many intriguing evolutionary questions, such as how these dynamic Chromosomes arise and why their content differs from autosomes. Recently, empirical evidence has built on theoretical work and comparisons of XY and ZW systems are set to provide further insight. Sex Chromosomes are unusually labile systems, with frequent shifts between male and female heterogamety and with a large variety in the precise number and types of Chromosomes. The lability is further emphasized by rapid turnover of genes and gene organization on the Y Chromosome. All types of Sex Chromosome (X, Y, Z and W) contain ampliconic structures of multi-copy genes. A common model of Sex-Chromosome evolution implies gradual cessation of recombination between the proto-Sex Chromosomes. The gene content of the X Chromosome and the Z Chromosome is unusual, with a non-random representation of genes with Sex-biased gene expression. The molecular evolution of Sex-linked genes differs from autosomal genes with respect to mutation rate and selective pressure. It is now clear that Sex Chromosomes differ from autosomes in many aspects of genome biology, such as organization, gene content and gene expression. Moreover, Sex linkage has numerous evolutionary genetic implications. Here, I provide a coherent overview of Sex-Chromosome evolution and function based on recent data. Heteromorphic Sex Chromosomes are almost as widespread across the animal and plant kingdoms as Sexual reproduction itself and an accumulating body of genetic data reveals interesting similarities, as well as dissimilarities, between organisms with XY or ZW Sex-determination systems. Therefore, I discuss how patterns and processes associated with Sex linkage in male- and female-heterogametic systems offer a useful contrast in the study of Sex-Chromosome evolution.

  • Sex-Chromosome evolution: recent progress and the influence of male and female heterogamety
    Nature Reviews Genetics, 2011
    Co-Authors: Hans Ellegren
    Abstract:

    It is now clear that Sex Chromosomes differ from autosomes in many aspects of genome biology, such as organization, gene content and gene expression. Moreover, Sex linkage has numerous evolutionary genetic implications. Here, I provide a coherent overview of Sex-Chromosome evolution and function based on recent data. Heteromorphic Sex Chromosomes are almost as widespread across the animal and plant kingdoms as Sexual reproduction itself and an accumulating body of genetic data reveals interesting similarities, as well as dissimilarities, between organisms with XY or ZW Sex-determination systems. Therefore, I discuss how patterns and processes associated with Sex linkage in male- and female-heterogametic systems offer a useful contrast in the study of Sex-Chromosome evolution.

Megan E Mcauliffe - One of the best experts on this subject based on the ideXlab platform.

Susan A Korrick - One of the best experts on this subject based on the ideXlab platform.

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