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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.

Gene Flow

Gene Flow

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

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.

What is Population Genetics?

What is Population Genetics?

A population is composed of members of the same species that simultaneously live and interact in the same area. When individuals in a population breed, they pass down their genes to their offspring. Many of these genes are polymorphic, meaning that they occur in multiple variants. Such variations of a gene are referred to as alleles. The collective set of all the alleles within a population is known as the gene pool.

Genome Size and the Evolution of New Genes

Genome Size and the Evolution of New Genes

While every living organism has a genome of some kind (be it RNA, or DNA), there is considerable variation in the sizes of these blueprints. One major factor that impacts genome size is whether the organism is prokaryotic or eukaryotic. In prokaryotes, the genome contains little to no non-coding sequence, such that genes are tightly clustered in groups or operons sequentially along the chromosome. Conversely, the genes in eukaryotes are punctuated by long stretches of non-coding sequence.

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Related Experiment Video

Updated: Jun 6, 2025

High-Throughput Live Imaging of Microcolonies to Measure Heterogeneity in Growth and Gene Expression

High-Throughput Live Imaging of Microcolonies to Measure Heterogeneity in Growth and Gene Expression

Published on: April 18, 2021

Asynchronous abundance fluctuations can drive giant genotype frequency fluctuations.

Joao A Ascensao^1,2, Kristen Lok^1,3, Oskar Hallatschek^4,5,6

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

Nature Ecology & Evolution

|November 23, 2024

Summary

Large population fluctuations can cause significant genotype frequency changes when different genotypes fluctuate asynchronously. This asynchronous fluctuation, termed decoupling noise, impacts evolution beyond genetic drift.

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Last Updated: Jun 6, 2025

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Area of Science:

Ecology
Evolutionary Biology
Population Dynamics

Background:

Stochastic population abundance fluctuations are common and affect population dynamics.
Abundance fluctuations with a Taylor's law exponent of two are not typically considered to strongly influence evolution.

Purpose of the Study:

To investigate if asynchronous abundance fluctuations between genotypes can lead to significant genotype frequency fluctuations.
To develop a model explaining the mechanisms behind these fluctuations and their evolutionary impact.

Main Methods:

Serial dilution experiments with mixed Escherichia coli strains.
Development of an effective model for population and genotype frequency fluctuations.
Analysis of Saccharomyces cerevisiae populations for decoupling noise.

Main Results:

Asynchronous abundance fluctuations led to genotype frequency fluctuations exceeding expectations from genetic drift.
A model demonstrated that decoupling in offspring number correlations between genotypes drives these large frequency fluctuations.
Chaotic dynamics may underlie the observed excess frequency fluctuations.

Conclusions:

Decoupling noise, arising from asynchronous fluctuations, significantly impacts evolutionary outcomes independently of genetic drift.
This phenomenon is likely widespread across diverse biological populations due to its generic nature.