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Related Concept Videos

Inheritance of Chromatin Structures03:17

Inheritance of Chromatin Structures

Epigenetics is the study of inherited changes in a cell's phenotype without changing the DNA sequences. It provides a form of memory for the differential gene expression pattern to maintain cell lineage, position-effect variegation, dosage compensation, and maintenance of chromatin structures such as telomeres and centromeres. For example, the structure and location of the centromere on chromosomes are epigenetically inherited. Its functionality is not dictated or ensured by the underlying DNA...
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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 most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.
X-linked Traits01:19

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In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.

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Accelerated adaptive evolution on a newly formed X chromosome.

Doris Bachtrog1, Jeffrey D Jensen, Zhi Zhang

  • 1Department of Integrative Biology, University of California, Berkeley, Berkeley, California, USA. dbachtrog@berkeley.edu

Plos Biology
|May 1, 2009
PubMed
Summary

Newly formed X chromosomes show rapid adaptive evolution, with significantly more genes undergoing beneficial mutations compared to older X chromosomes. This suggests active adaptation during sex chromosome differentiation.

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Area of Science:

  • Evolutionary biology
  • Genomics
  • Population genetics

Background:

  • Sex chromosomes evolve from autosomes, typically involving gene loss from the Y chromosome.
  • The evolutionary dynamics of newly formed sex chromosomes are less understood than those of older systems.

Purpose of the Study:

  • To investigate adaptive evolution on a recently formed neo-X chromosome in Drosophila miranda.
  • To compare selection patterns on the neo-X chromosome with the ancestral X chromosome.

Main Methods:

  • Comparative analysis of DNA sequence variation between neo-X and ancestral X genes.
  • Statistical tests to identify genes under recent directional selection.
  • Estimation of adaptation rates and fitness effects of substitutions.

Main Results:

  • Reduced synonymous diversity on the neo-X suggests recent directional selection.
  • 10-15% of neo-X genes show evidence of recent adaptive evolution, versus 1-3% on the ancestral X.
  • Higher rates and stronger fitness effects of adaptation observed on the neo-X.

Conclusions:

  • Newly formed X chromosomes actively adapt, not passively evolve.
  • Adaptive evolution on the neo-X responds to sex-biased transmission and Y chromosome degeneration.
  • Mechanisms may include gene content changes and dosage compensation evolution.