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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,...

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).

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.

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.

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.

Background and Environment Affect Phenotype

Background and Environment Affect Phenotype

Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as temperature, oxygen availability, presence of mutagens, that can alter an organism’s phenotype.
An example of how genetic background affects phenotype can be seen in horses. The Extension gene in horses is responsible for their coat color. A wild-type gene (EE) produces black pigment in the coat, while a mutant gene (ee) produces red pigment. A...

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Related Experiment Video

Updated: Aug 20, 2025

A Concoction Pipeline for Generating Molecular Operational Taxonomic Units (MOTUs) Among Riparian and Aquatic Beetles

A Concoction Pipeline for Generating Molecular Operational Taxonomic Units (MOTUs) Among Riparian and Aquatic Beetles

Published on: July 11, 2025

Microgeographical Variation in Allozyme Frequencies in Avena barbata.

J L Hamrick¹, R W Allard

¹Department of Genetics, University of California, Davis, Calif. 95616.

Proceedings of the National Academy of Sciences of the United States of America

|August 1, 1972

Summary

Genetic variation in A. barbata populations reveals nonrandom allele distribution. These microgeographical patterns correlate with habitat and parallel broader climatic zones, supporting Neo-Darwinian evolution driven by selection.

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Area of Science:

Population Genetics
Evolutionary Biology
Ecology

Background:

Understanding microgeographical patterns of genetic variation is crucial for evolutionary studies.
Avena barbata populations inhabit diverse ecological niches, offering insights into adaptation.

Purpose of the Study:

To determine the microgeographical distribution of alleles in Avena barbata populations.
To investigate the correlation between allele distribution and habitat characteristics.
To evaluate evolutionary models explaining observed genetic patterns.

Main Methods:

Analysis of allele frequencies for five enzyme loci and one morphological variant.
Sampling of Avena barbata populations across transitional vegetational zones.
Spatial analysis of genetic variation in relation to habitat features.

Main Results:

Nonrandom spatial distribution of alleles was observed within A. barbata populations.
Allele distribution showed a strong correlation with local habitat conditions.
Patterns of microgeographical variation mirrored those found in major climatic zones of California.

Conclusions:

The observed genetic patterns are best explained by Neo-Darwinian evolutionary models.
Natural selection plays a predominant role in shaping allele frequencies at a microgeographical scale.
Habitat-specific selection drives adaptive genetic variation in Avena barbata.