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Allele Frequency – Introduction Factors and Examples

Grade 10
May 4, 2023

Allele Frequency

The allele frequency represents the incidence of gene variation in a population. Alleles are different variants of a gene that are found on the same chromosome at the same place or genetic locus. The frequency of an allele is calculated by dividing the number of times an allele of interest is discovered in a population by the total number of copies of all the alleles at that specific genetic locus in the population. Allele frequency can be expressed as a decimal, a percentage, or a fraction.

Allele frequencies in a population represent genetic variety. Alle frequency changes over time might reflect genetic drift or the introduction of new mutations into the population. The allele frequency differs from the phenotypic ratio in that it considers all alleles, even recessive alleles that are “hidden” inside carrier species.

The phenotypic ratio solely defines the phenotypes, or real physical characteristics, that exist in a population. To determine the frequency of an allele, scientists must include heterozygous individuals who may be carrying a recessive gene.

The Hardy-Weinberg equation defines the connection between two alleles within a population and is most typically used to compute allele frequency. However, when more than two alleles are present, scientists must apply more complicated procedures to estimate the true allele frequency. In addition, allele frequency can alter over time as a population responds to evolution by increasing or lowering the frequency of specific alleles.


Allele frequency

  • Calculating allele frequencies is a difficult issue that mixes math and genetics. In most cases, all the alleles in a population sum up to 100%. As a result, we may apply mathematical formulae to forecast and determine an allele’s frequency in a population.
  • Examine all phenotypes to determine the number of alleles in a particular population. The phenotypes that reflect the allele are frequently hidden by the interaction of dominant and recessive alleles. Scientists use the Hardy-Weinberg (HW) equation to examine the allele frequency in a population. The Hardy-Weinberg equation looks like this:
  • p2 + 2pq + q2 = 1
  • P and q represent the allele frequency of certain alleles. The frequency of the homozygous dominant genotype is represented by the word p2. The frequency of the homozygous recessive genotype is represented by the other term, q2.
  • While counting all of the hidden alleles is hard, counting the number of recessive phenotypes in a population is simple. Two recessive alleles create recessive phenotypes. As a result, dividing the total number of recessive phenotypes by the total number of individuals yields q2. Next, let’s look at how we can utilize this data to compute the allele frequency of every given allele. 
  • p2 + 2pq + q2 = 1 

Calculation of Allele frequency

Calculation Example

Assume there are 100 people in a population with two types of alleles, B for blue eyes and G for green eyes. Because each person has two copies of each allele, multiply two by 100 to get the total number of allele copies in the population.

Numerous genes code for human eye color in real life, but in this case, there are only three distinct allele combinations in this gene pool: BB, BG, and GG. Then, for each allele type, count the number of persons in the population. While genotypic frequencies examine gene expression, allele frequencies examine the frequency with which a certain allele appears in a population.

In this example, multiply 50 by two because there are two B’s in the BB genotype to determine the allele frequency of B.


Then, because everyone with the BG genotype has a B allele, there are a total of 123 B alleles. Finally, divide 123 by 200 because each individual in the group contains two alleles, yielding an allele frequency of 0.615, or 61.5 percent.

Then repeat the process for the G allele. By multiplying the 27 persons with GG alleles by two and adding the 23 people who also have a G allele, we get 0.385 or 38.5 percent when we divide this figure, 77, by 200.

Check for errors by ensuring that all allele frequencies sum up to 1 or 100 percent. In this case, 61.5 multiplied by 38.5 equals 100.

Factors Act to Change Allele Frequency 

  • If the frequency of alleles in a population changes, it indicates an evolutionary shift.
  • Five variables influence genetic equilibrium and cause population heterogeneity. These are:
  1. Mutations
  2. Recombination of genes
  3. Gene migration or gene flow
  4. Genetic drift
  5. Natural selection

Alleles responsible for Different eye color

1. Mutations:

  • These are substantial, rapid alterations in the genetic material that are inherited.
  •  Mutations are a random process that can occur in either direction.
  • The majority of mutations are either detrimental or neutral.
  • The mutation rate is quite low.
  • Mutations generate and sustain variety within a population and contribute new genes and alleles to a gene pool.
  • Speciation can occur as a result of the accumulation of mutations over several.

Mutation in genes

2. Recombination of Genes:

  • Recombination includes the reshuffling of chromosomal genes.
  • The possibilities of recombination are higher in species that reproduce sexually and in those that go through gametogenesis followed by fertilization.
  • Recombination results in the redistribution of distinct features to different people in a population, despite only the reshuffling of already existing characters occurring, and no new genes are generated.

3. Gene Drift:

  • It is the random variation in allele frequency caused by chance fluctuations.

4. Gene Migration (gene flow):

When two populations are genetically distinct, even a small quantity of immigration can result in significant changes in allele frequencies. When migratory individuals contact members of the local population, a process known as hybridization occurs; numerous novel alleles may be introduced into the host population’s local gene pool. This is referred to as gene migration. Gene flow refers to adding or removing alleles when people arrive or depart a population from another location.

5. Natural Selection:

Natural selection is the process by which nature favors substantially better-suited individuals over less-adapted individuals in a diverse population.

Rise of an Allele frequency due to Natural selection

Allele Frequency


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