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Related Concept Videos

Types of Selection01:46

Types of Selection

Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an...
Frequency-dependent Selection01:21

Frequency-dependent Selection

When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.Positive Frequency-Dependent SelectionIn positive...
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.In the early 20th century,...
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...
Genetics of Speciation02:16

Genetics of Speciation

Speciation is the evolutionary process resulting in the formation of new, distinct species—groups of reproductively isolated populations.The genetics of speciation involves the different traits or isolating mechanisms preventing gene exchange, leading to reproductive isolation. Reproductive isolation can be due to reproductive barriers that have effects either before or after the formation of a zygote. Pre-zygotic mechanisms prevent fertilization from occurring, and post-zygotic mechanisms...
Gene Flow02:39

Gene Flow

Gene flow is the transfer of genes among populations, resulting from either the dispersal of gametes or from the migration of individuals.

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Related Experiment Video

Updated: Jun 23, 2026

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

Published on: August 18, 2023

The conditional ancestral selection graph with strong balancing selection.

John Wakeley1, Ori Sargsyan

  • 1Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA. wakeley@fas.harvard.edu

Theoretical Population Biology
|April 18, 2009
PubMed
Summary
This summary is machine-generated.

Strong balancing selection between alleles leads to a neutral structured coalescent model. This finding, supported by simulations, simplifies understanding of ancestral processes in population genetics.

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Area of Science:

  • Population Genetics
  • Evolutionary Biology
  • Mathematical Biology

Background:

  • The ancestral selection graph models the evolutionary history of populations.
  • Understanding the impact of strong selection on these graphs is crucial for evolutionary inference.

Purpose of the Study:

  • To analyze the behavior of the conditional ancestral selection graph under strong balancing selection.
  • To investigate the convergence of the ancestral process in limiting cases of selection and mutation.

Main Methods:

  • Heuristic separation-of-time-scales argument.
  • Mathematical analysis in the limit of infinite selection strength.
  • Computer simulations to validate theoretical results.
  • Rigorous demonstration for the limit of infinite mutation rate.

Main Results:

  • The ancestral process converges to a neutral structured coalescent with strong balancing selection.
  • Mutation effectively acts as migration between allele-specific subpopulations.
  • The neutral conditional ancestral process converges to the Kingman coalescent with infinite mutation rate.

Conclusions:

  • Strong balancing selection simplifies complex ancestral processes into neutral models.
  • The study provides a theoretical framework and computational support for these simplifications.
  • Results align with and extend previous findings in population genetics theory.