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Related Concept Videos

Dosage Compensation02:50

Dosage Compensation

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In animals, gender is determined by the number and type of sex chromosome. For example, human females have two X chromosomes, and males have one X and one Y chromosome, whereas C.elegans with one X chromosome is a male, and the one with two X chromosomes is a hermaphrodite.
In addition to sexual development, the X chromosome has genes involved in autosomal functions such as brain development and the immune system. Therefore, males and females with  distinct numbers of X chromosomes will...
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The Ratio of X Chromosome to Autosomes02:45

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In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomes. The Y chromosome in Drosophila is active but does not determine sex. It contains genes responsible for the production of sperms in adult flies.  
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female...
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X and Y Chromosomes02:32

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Among mammals, the gender of an organism is determined by the sex chromosomes. Humans have two sex chromosomes, X and Y. Every human diploid cell has 22 pairs of autosomes and one pair of sex chromosomes. A human female has two X chromosomes, while a male has one X chromosome and one Y chromosome.
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In 1866, Gregor Mendel published the results of his pea plant breeding experiments, providing evidence for predictable patterns in the inheritance of physical characteristics. The significance of his findings was not immediately recognized. In fact, the existence of genes was unknown at the time. Mendel referred to hereditary units as “factors.”
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Nondisjunction01:29

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During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed sister chromatid separation during meiosis II. In some species, notably plants, nondisjunction can result in an organism with an entire additional set of chromosomes, which is called polyploidy. In humans, nondisjunction can occur during male or female gametogenesis and the resulting gametes possess one too many or one too few chromosomes.
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Nondisjunction01:21

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Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate correctly and move to the opposite poles of the cells. This produces daughter cells with abnormal chromosome numbers.  Nondisjunction is common during anaphase I or anaphase II of meiosis.  Mutations in synaptonemal complex proteins that attach homologous chromosomes increase the chances of nondisjunction in anaphase I of meiosis I. In contrast, mutations in topoisomerases and condensins that hold...
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When and why does sex chromosome dosage compensation evolve?

Christopher H Chandler1

  • 1Department of Biological Sciences, State University of New York at Oswego, Oswego, New York.

Annals of the New York Academy of Sciences
|January 19, 2017
PubMed
Summary

Dosage compensation mechanisms evolve unevenly across species due to varying definitions and a lack of universal application. This review explores testing methods and phylogenetic patterns of gene dosage regulation.

Keywords:
dosage compensationsex chromosomes

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Area of Science:

  • Genetics and Genomics
  • Evolutionary Biology
  • Molecular Biology

Background:

  • Sex determination in many species relies on sex chromosomes (X/Z and Y/W), leading to gene dosage imbalances.
  • The non-recombining Y or W chromosome typically degenerates and carries fewer genes than its X or Z counterpart.
  • Early research in model organisms suggested widespread evolution of regulatory mechanisms for balanced X-linked gene expression.

Purpose of the Study:

  • To clarify the reasons behind the uneven evolution of dosage compensation mechanisms across different species.
  • To discuss current methodologies for detecting sex chromosome dosage compensation.
  • To examine the phylogenetic distribution and potential explanations for dosage compensation patterns.

Main Methods:

  • Review and synthesis of existing literature on sex chromosome dosage compensation.
  • Analysis of different definitions and perceptions of dosage compensation (e.g., all-or-nothing vs. variable).
  • Exploration of phylogenetic patterns and evolutionary drivers of dosage compensation.

Main Results:

  • Dosage compensation mechanisms are not universal and their evolution is complex.
  • Confusion in the field stems from varied definitions and viewing dosage compensation as binary.
  • Dosage compensation can vary across cell types, developmental stages, and gene classes.

Conclusions:

  • Understanding the variability and phylogenetic distribution of dosage compensation is crucial.
  • Methods exist to test for dosage compensation in non-model organisms.
  • Future research should focus on comparative analyses and refining testing approaches.