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A direct experimental test of Ohno's hypothesis.

Ljiljana Mihajlovic1, Bharat Ravi Iyengar2,3, Florian Baier1

  • 1Department of Fundamental Microbiology, University of Lausanne, Lausanne, Switzerland.

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Gene duplication allows genes to tolerate mutations, fostering evolutionary diversity. While gene duplicates showed increased robustness and diversity, phenotypic evolution was not accelerated, highlighting gene dosage importance.

Keywords:
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Area of Science:

  • Evolutionary biology
  • Molecular evolution
  • Genetics

Background:

  • Gene duplication is a key driver of evolutionary innovation, providing new genetic material for novel protein functions.
  • Ohno's hypothesis suggests gene duplication facilitates new phenotypes by allowing genes to tolerate mutations.
  • Competing theories propose that deleterious mutations rapidly inactivate gene duplicates, limiting their evolutionary potential.

Purpose of the Study:

  • To experimentally test Ohno's hypothesis on gene duplication and evolution.
  • To investigate the impact of gene copy number on evolutionary dynamics and mutational robustness.
  • To explore the role of gene dosage in the evolution of new phenotypes.

Main Methods:

  • Evolving populations of Escherichia coli with either one or two copies of a fluorescent protein gene.
  • Employing high-throughput DNA sequencing to analyze genotypic evolution.
  • Utilizing biochemical assays and engineering of selected variants to assess phenotypic changes.

Main Results:

  • Populations with two gene copies exhibited greater mutational robustness compared to single-copy populations.
  • Double-copy populations showed relaxed purifying selection, increased genetic and phenotypic diversity, and earlier accumulation of beneficial mutations.
  • Despite increased diversity, phenotypic evolution was not accelerated, potentially due to rapid inactivation of one gene copy.

Conclusions:

  • Experimental results support Ohno's hypothesis regarding increased mutational robustness from gene duplication.
  • Findings suggest that gene dosage plays a crucial role, potentially offering an alternative explanation to Ohno's original hypothesis.
  • The study provides a valuable experimental framework for testing models of evolution by gene duplication.