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Related Concept Videos

Frequency-dependent Selection

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.

Types of Selection

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...

Hardy-Weinberg Principle

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.

Multiple Allele Traits

Multiple Allele Traits

The Concept of Multiple Allelism

Mutation, Gene Flow, and Genetic Drift

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).

Genetic Drift

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.

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Related Experiment Video

Updated: May 27, 2026

Following the Dynamics of Structural Variants in Experimentally Evolved Populations

Following the Dynamics of Structural Variants in Experimentally Evolved Populations

Published on: February 3, 2023

Quantifying selection acting on a complex trait using allele frequency time series data.

Christopher J R Illingworth¹, Leopold Parts, Stephan Schiffels

¹Wellcome Trust Sanger Institute, Hinxton, Cambridge, United Kingdom.

Molecular Biology and Evolution

|November 25, 2011

Summary

This summary is machine-generated.

This study introduces a population genetics method to analyze allele frequency changes over time in populations under selection. The method identified 6% of sites evolving nonneutrally in yeast under heat stress, revealing drivers of adaptation.

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Area of Science:

Population genetics
Evolutionary biology
Genomics

Background:

Beneficial alleles increase in frequency in large, genetically diverse populations under selection.
Allele frequency changes can map quantitative trait loci (QTLs).

Purpose of the Study:

To develop a population genetic method for analyzing time-series allele frequency data.
To identify and quantify selective effects and drivers of adaptation in yeast under heat stress.

Main Methods:

Formulating equations of motion for allele frequencies based on evolutionary theory.
Deriving likelihoods for sequencing data under various evolutionary scenarios.
Analyzing time-series allele frequency data from a yeast cross propagated under heat stress.

Main Results:

Approximately 6% of polymorphic sites evolved nonneutrally under heat stress.
Identified 44 genomic regions with candidate driver alleles and quantified their selective advantage.
Estimated recombination rates and demonstrated selection signatures beyond additive models.

Conclusions:

The developed method provides insights into prevailing evolutionary dynamics.
The study identified specific genomic regions and alleles under strong selection in yeast.
The approach is broadly applicable to studying adaptation in diverse systems under various evolutionary pressures.