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Related Experiment Video

Updated: Feb 10, 2026

Molecular Evolution of the Tre Recombinase
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The evolution of genetic drift over 50,000 generations.

Joao A Ascensao1,2, QinQin Yu3,4, Oskar Hallatschek3,5,6

  • 1Department of Bioengineering, University of California Berkeley, Berkeley, CA, USA.

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|February 9, 2026
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Summary

Genetic drift, random variation in reproductive success, can evolve over time. This study shows the variance in descendant numbers diverged between E. coli populations, impacting mutation establishment and adaptation.

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Area of Science:

  • Evolutionary biology
  • Population genetics
  • Microbial evolution

Background:

  • Genetic drift, driven by random variation in reproductive success, is a key factor shaping genetic diversity and evolution.
  • The strength of genetic drift is determined by the variance in descendant number, which influences evolutionary outcomes like mutation establishment.
  • It was unclear if the variance in descendant number itself evolves over long timescales.

Purpose of the Study:

  • To investigate whether the variance in descendant number, a key parameter of genetic drift, evolves over long timescales.
  • To disentangle the contributions of census population size and variance in descendant number to effective population size.
  • To analyze the divergent evolution of genetic drift in two replicate populations of E. coli.

Main Methods:

  • Utilized model-based Bayesian inference combined with joint tracking of neutral lineage frequency fluctuations and census population sizes.
  • Analyzed data from 33 clones across 50,000 generations in the E. coli Long-Term Evolution Experiment (two replicate populations: Ara-2 and Ara+2).
  • Quantified changes in census size and variance in descendant number to infer effective population size and drift strength.

Main Results:

  • The strength of genetic drift evolved markedly and divergently between the two replicate E. coli populations.
  • Both census size and variance in descendant number changed substantially over time, with variance in descendant number driving most changes in effective population size.
  • After ~2,000 generations, the variance in descendant number diverged, with Ara-2 exhibiting 1.5-5x stronger drift than expected, indicating evolved increased stochasticity.

Conclusions:

  • The key parameter governing genetic drift (variance in descendant number) can itself evolve.
  • Divergent evolution of genetic drift has direct consequences for the rate and probability of adaptation.
  • Beneficial mutations are approximately twice as likely to establish in the Ara+2 population compared to Ara-2 due to differences in drift strength.