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Related Concept Videos

Dosage Compensation02:50

Dosage Compensation

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 have...
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Hybrid Zones

Hybrid zones are narrow regions where two closely related species interact, mate, and produce hybrids. Relative to either parent species, hybrids may possess distinct phenotypic or genetic differences that impact their survival and reproductive success. The genetic variances introduced by hybridization influence species diversity and speciation processes within the hybrid zone.Gene flow and natural selection are evolutionary mechanisms that shape the outcome of a hybrid zone. Gene flow...
X and Y Chromosomes02:32

X and Y Chromosomes

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In 1928, a German botanist Emil Heitz observed the moss nuclei with a DNA binding dye. He observed that while some chromatin regions decondense and spread out in the interphase nucleus, others do not. He termed them euchromatin and heterochromatin, respectively. He proposed that the heterochromatin regions reflect a functionally inactive state of the genome. It was later confirmed that heterochromatin is transcriptionally repressed, and euchromatin is transcriptionally active chromatin.
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Genotyping and Quantification of In Situ Hybridization Staining in Zebrafish
05:41

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Published on: January 28, 2020

Why does dosage compensation differ between XY and ZW taxa?

Sara Naurin1, Bengt Hansson, Staffan Bensch

  • 1Department of Animal Ecology, Ecology Building, Lund University, SE-22362 Lund, Sweden. Sara.Naurin@zooekol.lu.se

Trends in Genetics : TIG
|December 8, 2009
PubMed
Summary

ZW females exhibit incomplete dosage compensation due to male-adapted genes on Z chromosomes. This sex determination system shows extensive male gene expression bias, unlike XY systems.

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Area of Science:

  • Evolutionary genetics
  • Sex determination systems
  • Gene expression regulation

Background:

  • Species with ZW sex determination (e.g., birds) show significant male bias in Z chromosome gene expression.
  • This suggests incomplete dosage compensation in ZW females.
  • Existing research highlights discrepancies in sex-biased gene expression and dosage compensation between ZW and XY systems.

Purpose of the Study:

  • To propose a functional explanation for the extensive male bias in Z chromosome gene expression in ZW systems.
  • To investigate the extent of dosage compensation achieved by ZW females.
  • To contrast ZW and XY sex determination systems regarding gene expression and dosage compensation.

Main Methods:

  • Comparative analysis of gene expression patterns on Z chromosomes in ZW systems.
  • Theoretical modeling of evolutionary pressures (sexual selection, mutation bias) on Z-linked genes.
  • Literature review comparing ZW and XY dosage compensation mechanisms.

Main Results:

  • The male bias on Z chromosomes is attributed to the functional properties of male-adapted genes, making them less suitable for high expression in females.
  • ZW females appear to achieve partial dosage compensation, sufficient for maintaining critical network integrity.
  • Z chromosomes spend more evolutionary time in males, intensifying sexual selection and mutation bias, leading to greater male-biased expression.

Conclusions:

  • Functional constraints of male-adapted genes contribute significantly to Z-linked gene expression bias in ZW systems.
  • ZW females achieve a level of dosage compensation adequate for biological function, despite incomplete compensation.
  • Differences in evolutionary pressures and chromosomal transmission in ZW versus XY systems explain observed variations in gene expression and dosage compensation.