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Related Concept Videos

Genetic Drift03:33

Genetic Drift

Natural selection—probably the most well-known evolutionary mechanism—increases the prevalence of traits that enhance survival and reproduction. However, evolution does not merely propagate favorable traits, nor does it always benefit populations.
Limits to Natural Selection01:38

Limits to Natural Selection

Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.
Mutation, Gene Flow, and Genetic Drift01:09

Mutation, Gene Flow, and Genetic Drift

In a population that is not at Hardy-Weinberg equilibrium, the frequency of alleles changes over time. Therefore, any deviations from the five conditions of Hardy-Weinberg equilibrium can alter the genetic variation of a given population. Conditions that change the genetic variability of a population include mutations, natural selection, non-random mating, gene flow, and genetic drift (small population size).
Hardy-Weinberg Principle01:49

Hardy-Weinberg Principle

Diploid organisms have two alleles of each gene, one from each parent, in their somatic cells. Therefore, each individual contributes two alleles to the gene pool of the population. The gene pool of a population is the sum of every allele of all genes within that population and has some degree of variation. Genetic variation is typically expressed as a relative frequency, which is the percentage of the total population that has a given allele, genotype or phenotype.
Survival Tree01:19

Survival Tree

Survival trees are a non-parametric method used in survival analysis to model the relationship between a set of covariates and the time until an event of interest occurs, often referred to as the "time-to-event" or "survival time." This method is particularly useful when dealing with censored data, where the event has not occurred for some individuals by the end of the study period, or when the exact time of the event is unknown.
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Evolution of New Traits in Microbes01:24

Evolution of New Traits in Microbes

Microorganisms evolve rapidly due to their large population sizes and short generation times, often exhibiting measurable changes within days under laboratory conditions. Natural selection acts on standing genetic variation, enabling the retention and amplification of beneficial traits that confer fitness advantages in changing environments.Adaptive Pigment Regulation in RhodobacterIn Rhodobacter, a genus of purple non-sulfur bacteria, light-harvesting pigments such as bacteriochlorophyll and...

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Related Experiment Video

Updated: Jun 1, 2026

Daily Transfers, Archiving Populations, and Measuring Fitness in the Long-Term Evolution Experiment with Escherichia coli
15:00

Daily Transfers, Archiving Populations, and Measuring Fitness in the Long-Term Evolution Experiment with Escherichia coli

Published on: August 18, 2023

Hidden randomness between fitness landscapes limits reverse evolution.

Longzhi Tan1, Stephen Serene, Hui Xiao Chao

  • 1Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. tantan@mit.edu

Physical Review Letters
|June 15, 2011
PubMed
Summary
This summary is machine-generated.

Reverse evolution, where adaptations are undone, is rare in bacteria. As genetic adaptations become more complex, reversing them becomes less likely, supporting a molecular version of Dollo's law.

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Related Experiment Videos

Last Updated: Jun 1, 2026

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Published on: August 18, 2023

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Area of Science:

  • Evolutionary biology
  • Microbial genetics

Background:

  • Adaptations to environmental pressures can sometimes be reversed.
  • Understanding the genetic basis of reverse evolution is crucial for evolutionary studies.

Purpose of the Study:

  • To investigate the genotypic underpinnings of reverse evolution in bacteria.
  • To determine how the complexity of genetic adaptations affects the possibility of reversal.

Main Methods:

  • Measured the fitness of E. coli strains with all combinations of five mutations in an antibiotic-resistance gene.
  • Assessed strain fitness in two distinct antibiotic environments.

Main Results:

  • Adaptations to one antibiotic environment typically reduced fitness in the other.
  • Reverse evolution was found to be infrequent and decreased with increasing adaptation complexity.

Conclusions:

  • The study suggests a probabilistic, molecular form of Dollo's law.
  • The complexity of genetic adaptations significantly constrains the potential for reverse evolution.