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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 Variation

Genetic Variation

Genetic variation is the diversity in DNA sequences found among individuals of the same species. This diversity is crucial for a species' survival because it helps organisms adapt to environmental changes. Genetic variation begins with fertilization, where an egg and sperm cell merge. Each of these cells carries 23 chromosomes, up to 46 in the fertilized egg. Chromosomes are long DNA strands that contain genes, the basic units of heredity.
Genes exist in different versions called alleles,...

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.

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.

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.

Genetics of Speciation

Genetics of Speciation

Speciation is the evolutionary process resulting in the formation of new, distinct species—groups of reproductively isolated populations.

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Following the Dynamics of Structural Variants in Experimentally Evolved Populations

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Published on: February 3, 2023

QUANTITATIVE GENETIC VARIANCE MAINTAINED BY FLUCTUATING SELECTION WITH OVERLAPPING GENERATIONS: VARIANCE COMPONENTS

Akira Sasaki¹, Stephen Ellner¹

¹Department of Biology, Faculty of Science, Kyushu University, Fukuoka, 812-81, Japan.

Evolution; International Journal of Organic Evolution

|June 2, 2017

Summary

Fluctuating selection in random environments can maintain genetic variance, especially with overlapping generations. This occurs when environmental changes exceed a threshold, leading to discrete allele distributions and significant genetic variation.

Keywords:

Hardy-Weinberg disequilibrium evolutionary genetic stability fluctuating selection linkage disequilibrium quantitative genetic variance storage effect

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Area of Science:

Quantitative genetics
Evolutionary biology
Population genetics

Background:

Understanding how genetic variation is maintained in populations is crucial for evolutionary studies.
Random environments and fluctuating selection present unique challenges to maintaining genetic diversity.
Additive genetic models without epistasis or dominance are foundational in quantitative genetics.

Purpose of the Study:

To investigate the conditions under which quantitative genetic variance-covariance can be sustained in a fluctuating random environment.
To analyze the role of overlapping generations and Gaussian stabilizing selection in maintaining genetic variation.
To derive expressions for standing variance-covariance components as a function of environmental and genetic parameters.

Main Methods:

Modeling quantitative genetic variance-covariance under overlapping generations and fluctuating Gaussian stabilizing selection.
Assuming additive gene action with arbitrary linkage and ignoring recurrent mutation.
Analyzing the discrete nature of genotype distributions in evolutionarily stable populations.

Main Results:

Nonzero genetic variance is maintained if environmental heterogeneity surpasses a specific threshold.
Explicit asymptotic expressions for variance-covariance components were derived near the threshold or with large generational overlap.
Above the threshold, populations exhibit significant genetic variance through linkage disequilibrium and gamete covariance (Hardy-Weinberg disequilibrium).

Conclusions:

Fluctuating selection is a key mechanism for maintaining genetic variance in changing environments.
Environmental variability directly influences the proportion of disequilibrium variances contributing to total genetic variance.
The study provides a theoretical framework for understanding genetic variation maintenance in dynamic ecological conditions.