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Mutational equilibrium model of genome size evolution.

Dmitri A Petrov1

  • 1Department of Biological Sciences, Stanford University, California 94025, USA. dpetrov@stanford.edu

Theoretical Population Biology
|August 9, 2002
PubMed
Summary

Genome size in animals evolves to a mutational equilibrium, balancing DNA deletion and insertion rates. This new model explains genome size variation, differing from adaptive and junk DNA theories.

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Area of Science:

  • Evolutionary Biology
  • Genomics
  • Molecular Biology

Background:

  • Existing models for genome size evolution, such as adaptive and junk DNA theories, rely on selection pressures.
  • These models do not fully explain observed empirical relationships between DNA loss rates and genome size.

Purpose of the Study:

  • To propose and describe a novel mutational equilibrium model for genome size evolution.
  • To differentiate this model from adaptive and junk DNA theories.
  • To provide an empirical basis for the mutational equilibrium model using animal genome data.

Main Methods:

  • Development of a theoretical model where genome size is determined by the balance between DNA deletion and insertion rates.
  • Analysis of empirical data on the relationship between the rate of DNA loss via small deletions and genome size in animals.
  • Mathematical modeling to describe the scaling relationships between deletion rates, insertion rates, and genome size.

Main Results:

  • A strong power-function correlation was found between the rate of mutational DNA loss (per base pair) and genome size in animals, with genome size scaling as a negative 1.3 power function of the deletion rate per nucleotide.
  • This empirical relationship is not predicted by adaptive or junk DNA theories but is consistent with a mutational equilibrium model.
  • The model suggests that DNA gain through large insertions scales as a quarter-power function of genome size, and DNA loss through small deletions increases linearly with genome size.

Conclusions:

  • Genome size in animals is maintained at a stable equilibrium by the balance of mutational forces (deletions and insertions), not primarily by selection.
  • Changes in the intrinsic rates of DNA loss through small deletions significantly contribute to long-term genome size variation in animals.
  • The mutational equilibrium model offers a new framework for understanding genome size evolution, with implications for mutational biases and their adaptive consequences.

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