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Related Concept Videos

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).Mechanisms of Genetic VariationThe original sources of genetic variation are mutations,...
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...
What is Natural Selection?01:32

What is Natural Selection?

Natural selection is an evolutionary process in which individuals with survival-promoting traits reproduce at higher rates. These favorable traits become more common within a population or species. Naturally selected traits initially arise via random genetic mutations. In order for selection to occur, there must be variation within a population, the trait controlling the variation must be heritable, and there must be an evolutionary advantage for variation in the trait.The Theory of Natural...
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.For one, natural selection can only act upon existing genetic variation. Hypothetically, redtusks may enhance elephant survival by deterring ivory-seeking poachers. However, if there are no gene variants—or alleles—for redtusks, natural selection cannot increase the prevalence of...
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.Life is not fair. A deer grazing contentedly in a field can have her meal cut tragically short by a bolt of lightning. If the doomed doe is one of only three in the population, 1/3 of the population’s gene pool is lost. Random events like this can...
The Evidence for Evolution02:55

The Evidence for Evolution

Genetic variations accumulating within populations over generations give rise to biological evolution. Evolutionary changes can result in the formation of novel varieties and entire new species. These changes are responsible for the diverse forms of life inhabiting the planet. The evidence for evolution suggests that all living organisms descended from common ancestors.The collection of fossils within sedimentary rocks give a record of common ancestry and often depicts the history of evolution.

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Related Experiment Video

Updated: Jun 26, 2026

Following the Dynamics of Structural Variants in Experimentally Evolved Populations
04:52

Following the Dynamics of Structural Variants in Experimentally Evolved Populations

Published on: February 3, 2023

Experimental evolution reveals natural selection on standing genetic variation.

Henrique Teotónio1, Ivo M Chelo, Martina Bradić

  • 1Instituto Gulbenkian de Ciência, Apartado 14, P-2781-901 Oeiras, Portugal. teotonio@igc.gulbenkian.pt

Nature Genetics
|January 13, 2009
PubMed
Summary

Reverse evolution in fruit flies showed selection at specific genetic loci, with no overall loss of allele diversity. Despite returning to ancestral adaptation levels, allele frequencies only partially reverted.

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Area of Science:

  • Evolutionary Biology
  • Population Genetics
  • Molecular Genetics

Background:

  • Genetic variation fuels evolution through mutation and recombination.
  • Understanding adaptation and reverse evolution in sexual organisms at the molecular level is limited.

Purpose of the Study:

  • To investigate molecular population genetics during experimental reverse evolution.
  • To analyze changes in single nucleotide polymorphism (SNP) frequencies in Drosophila melanogaster.

Main Methods:

  • Conducted 50 generations of experimental reverse evolution in Drosophila melanogaster.
  • Monitored SNP frequency changes across the third chromosome.
  • Assessed the impact of finite population size and natural selection on genotypes.

Main Results:

  • Observed evidence of natural selection acting on multiple genetic loci.
  • Found no general decrease or increase in allele diversity.
  • Demonstrated complete convergence to ancestral adaptation levels.
  • Observed only partial return of allele frequencies to ancestral states.

Conclusions:

  • Experimental reverse evolution reveals complex genetic dynamics.
  • Selection can occur without significant changes in overall allele diversity.
  • Adaptation and allele frequency changes are not always congruent during reverse evolution.