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Gene Frequency Estimation, Factors and Definition

Grade 10
May 4, 2023

Gene Frequency

Gene frequency can be defined as the proportion of distinct alleles of a gene in a population. Their frequencies in a specific generation rely on their frequencies in the preceding generation and the proportion of diverse genotypes in the total population.

If two alleles or genes govern two alleles or genes govern a character in any population, the frequency of these alleles or genes can be simply estimated by observing that character under homozygous and heterozygous conditions.

In a population, the frequency of an allele is calculated by dividing the number of occurrences of that allele by the total number of alleles at that gene locus.

Gene frequency is defined as the fraction of unique alleles of a gene in a random mating population. Therefore, it is sometimes referred to as the genetic frequency. In other words, gene frequency refers to the fraction of each type of allele at a certain locus in a random mating population. Gene frequencies are used to characterize the composition of a population.

Gene Frequency Estimation

Estimating gene frequencies in a population entails three critical procedures, which are outlined below:

  • Sampling: A random sample of individuals is taken from the random mating population under investigation. The sample size should be big enough to represent all of the people in a population.
  • Classification: Following sampling, people are classified into distinct groups for each gene,, and their numbers are tallied.
  • Gene frequency calculation: Assume a 100-person random sample was taken from a random mating population of four ‘O’ clock plants (Mirabilis jalapa). Out of those 100 plants, 30 had red flowers, 40 had pink flowers, and 30 had white flowers.

A population of N individuals in a diploid species contains 2N alleles for each gene locus. For example, if a specific gene contains two alleles, ‘A’ and ‘a,’ the number of A alleles equals twice the number of AA homozygotes plus the number of Aa heterozygotes because each homozygote possesses two ‘A’ alleles. In contrast, each heterozygote possesses one ‘A’ allele.

Thus, the frequency of ‘A’ equals the number of ‘A’ alleles divided by the total number of alleles, i.e., 2N.

Difference between Allele frequency and Gene frequency

If the number is indicated by ‘n,’ the equation is as follows:

Estimation of Gene frequency


It is important to note that the overall frequency for all alleles will always be 1,

 i.e., p + q = 1 and nA + na = 2N.

Genotype Frequency and Hard-Weinberg Equilibrium

The gene and genotype frequencies in a randomly mated Mendelian population approach the equilibrium in a single generation. The Hardy-Weinberg equilibrium rule asserts that if there is no selection, mutation, migration, or genetic drift, a Mendelian population’s gene and genotype frequencies stay constant generation after generation.

Homozygotes (AA & aa) are created by combining gametes with comparable alleles. For example, aFor example, a male gamete carrying allele A (frequency p) will fuse with a female gamete carrying ‘A’ (also frequency p) at p x p = p2.

Similarly, the frequency with which a male gamete carrying allele ‘a’ (frequency q)” fuses with a female gamete carrying ‘a’ is q x q = q2.

Heterozygotes (Aa) are formed by fusing gametes with distinct alleles; the frequency with which a male gamete with allele ‘A’ fuses with a female gamete with allele ‘a’ is p x q = pq. Similarly, the frequency with which a female gamete carrying allele ‘A’ fuses with a male gamete carrying ‘a’ is p x q = pq. As a result, the total number of heterozygotes will be two pq.

Hardy-Weinberg relation

Factors Affecting Gene Frequency

Populations fluctuate throughout time. Individuals in a population may increase or decrease in number based on food supplies, climate, weather, and the availability of breeding grounds, among other factors. In addition, aIn addition, a population can vary genetically due to mutation, migration, selection, and random genetic drift.

These natural processes affect allele frequencies, altering the population’s essential composition.

  • Mutations result in the creation of new alleles, albeit the rate of mutation is insignificant. In the instance of harmful mutation, selection mitigates the effect.
  • Migration alters frequency distributions because immigrants from various populations have distinct genetic make-ups. As a result, gene frequency fluctuates in a certain community due to genotype changes caused by unequal emigration from other localities.
  • Selection decreases the fertility or survival of specific genotypes. Survival and reproductive ability are varied features in many populations. Some individuals may die before reproducing, while others may have a large number of offspring. Because of the unequal contribution of progeny, genes linked with greater fitness will become more common in a population.
  • Small differences from projected frequencies are caused by random genetic drift (chance difference), especially in small samples. These variances, however, are predicted and permitted by statistical testing.
  • Assortative mating of homozygotes and heterozygotes leads to an excess of homozygotes and heterozygotes, respectively, which affects the gene frequency.
  • The existence of subpopulations that are locally mating groups in a big population may be owing to ethnic factors or class grouping, as in humans, or to the restricted movement of some species in a vast region. Because of inbreeding, these occurrences increase the number of homozygotes.

Gene frequency vs Time

Gene Frequency


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