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Hardy Weinberg Law

Last updated date: 23rd Apr 2024
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Hardy Weinberg Law Notes

Before understanding the Hardy Weinberg law we must understand genetics in a very elaborate manner so the Core characteristics of the law is easily understandable by us.

Genetics can be called the scientific study of inherited variation in human beings, by this we can say that human genetics is the scientific study of inherited human variation.

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Why is it so important for us to understand and read about human genetics? One of the simplest explanations would be an interest in understanding ourselves better and allowing ourselves to know the composition of our body or the genetic composition of our body and the inheritance through which various predictions can be made. The study of human genetic variation is not confined to one thing, for but we learn about human genetics variation and its sources and transmission inevitably contributes to our understanding of genetics in general, by understanding the genetic composition and its variation in other species informs and expands our understanding of our own bodily compositions.


Another important reason for understanding human genetic variation is the discovery and description of the genetic contribution to many human diseases. The findings that we gather by studying genetic composition of a human body increases our motivation in light of our growing and understanding of the contribution that genes in particular make to the development of diseases such as cancer, heart disease, mental health illnesses and various other diseases and abnormalities. With the given perception and its realisations alongwith its discoveries of the previous 20 years have led to a evident increase in the number of people and organisations that are involved in human genetics.

Now there are similar explanations and contradictory explanations of the working of genetic variation but according to Hardy Weinberg equilibrium principle it is stated that the genetic variation in population will remain constant from one generation to the next in the absence of disturbing factors so in biological terms this theory explains that when meeting becomes random in a large population present with no disruptive circumstance, the law predicts that both genotype and alleles frequencies will remain constant because they are in perfect equilibrium.

This equilibrium can be distributed by a number of forces such as mutations, natural selection, non-random meeting, genetic drift and gene flow. For example, we know that mutations disrupt the equilibrium of allele frequencies by introducing new alleles into the population, in the same light, natural selection and non-random meeting disrupt the Hardy Weinberg equilibrium because the resultant changes in gene frequencies, this occurs majorly because certain alleles help or harm the reproductive success of the organisms that carry them. 

Another factor that can disrupt this equilibrium is genetic drift, now we all know that in small populations, phenomena occur by chance where allele frequencies grow higher or lower, this contributes to genetic drift, which can also be called genetic disruption. Gene flow, which occurs when breathing between two populations transfers new alleles into a population also leads on to alter the Hardy Weinberg equilibrium. Now with all these destructive forces which occur naturally and commonly in nature, the Hardy Weinberg equilibrium’s functioning is compromised and it is said that it can really be applied in reality, therefore, the Hardy Weinberg equilibrium is described as an idealised state and the genetic variations occurring in the nature can be measured as changes from this equilibrium state.

Any law that describes a phenomena occurring in the nature has several assumptions related to it, the Hardy Weinberg law also rests on multiple assumptions such as :

The population at hand or provided is large, and matings can be completely random when putting locus in reference.  

  • Allele frequencies remain constant over time because of the following:

  • There is no appreciable rate of new mutation.

  • The selection is not done against any particular genotype and individuals with all genotypes are equally capable of mating and passing on their genes.

In conclusion, a population which appears to meet these assumptions reasonably can be considered to be in the Hardy Weinberg equilibrium.

In the lack of any evolutionary influences onto another generation, the genotype and allele frequencies stay constant in a large, random-mating population. Influences include mate preference, genetic drift, mutation, gene flow, sexual choice, founder effect, genetic hitchhiking, meiotic drive, population bottleneck, inbreeding and assortative mating.


Genotype frequencies and allele frequencies are linked to one another in a way that certain allele frequencies are squarely extended. In other words, the Hardy Weinberg law states that the predicted frequency of genotypes can be calculated in a population below a certain restricted number of assumptions, given that the frequency of various alleles in a population has already been understood.


Consider a single locus carrying only two alleles represented by A and a with corresponding frequencies f(R) = p and f(r) = q respectively, then the genotype frequencies that can be assumed to be spontaneous mating under restricted conditions are


f(RR)= p2 for AA homozygotes


f(rr) = q2 for aa homozygotes


f(Rr) = 2pq for heterozygotes


The Hardy Weinberg equation is represented by the following equation:


p2 + q2 + 2pq = 1


In the exclusion of some kinds of factors including evolution, natural selection, genetic drift, etc. between one generation to another, the allele frequencies p and q tend to remain constant. This is how you can achieve equilibrium.


What is the Hardy Weinberg Principle?

The statute is named after G.H. Hardy and Wilhelm Weinberg. They were leaders in mathematically demonstrating this idea, also known as the Hardy-Weinberg equilibrium, law, model or theorem.


Hardy Weinberg principle is a theory which states that in the absence of disrupting factors, genetic diversity in a population would stay constant from one period to the next. In a large population with no destructive conditions, when mating is random, the law assumes that both genotype and allele frequencies will stay constant since they are in balance.


Hardy's work focused on debunking the view that existed in those days that a dominant allele tended to naturally increase in frequency.


Applications of Hardy Weinberg Law

Below mentioned are the applications of Hardy Weinberg law:-

The confusion over selection and dominance just isn't very exceptional in today's times. The Hardy-Weinberg genotype frequency tests are currently used to determine population stratification and other forms of non-random mating.

  • Genetic variations that change from mutation, genetic drift, migration, sexual selection and natural selection are persistently reflected by natural populations. A statistical criterion for a non-evolving population that can be contrasted with evolving populations is given by the Hardy-Weinberg rule.

  • Through this period, if the allele frequencies are recorded and calculated on the basis of the Hardy-Weinberg law values for the predicted frequencies, then it is possible to hypothesize operations that drive population evolution.

  • The law provides a template that is usually used to research the population genetics of diploid organisms as a point of origin that fulfills the common argument of a large population, random mating, no mutation, selection or migration.

  • However, for haploid pathogens, the Hardy-Weinberg model is not valid. Each of the principles in this law is thus broken in the case that a population is not discovered in the Hardy Weinberg equilibrium equation. 

  • This suggests that the population has been affected by selection, migration or non-random mating, where studies are taken out and theories are pursued in order to understand the mechanism behind its population's non-equilibrium.

Linkage Disequilibrium

Consider, for example, two or more alleles on the common chromosome, with 2 or more alleles in two separate loci. The frequency of allelic combinations reaches equilibrium as a consequence of genetic exchange through recombination occurring at regular intervals of time, across two syntenic loci.


Alleles are considered to be in a linkage disequilibrium if they are unable to reach an equilibrium, which is attributable to the inheritance of two or more connected alleles jointly, rather frequently than expected. These gene classes are known as supergenes as well.


Complete Dominance

In the case of total dominance, allele frequencies can be identified when Hardy-Weinberg equilibrium persists, where it would not be possible to distinguish among two genotypes. As a consequence of complete dominance of R over r, two genotypes RR and Rr sharing the same phenotype will help in deciding the allele frequencies from individual frequencies showing recessive phenotype rr. Here, the frequency of an individual should be equal to the frequency square of the recessive allele.


Significance of Hardy Weinberg Law

The significance of Hardy Weinberg law is that the model helps to evaluate the real genetic structure of a population over time. Only with the genetic composition, we would predict if the population was in equilibrium with Hardy-Weinberg (i.e., not evolving).


In evaluating the genetic variation present in a population, Hardy Weinberg law is essential and compares the real variation to the calculated value of Hardy Weinberg law if the population was in equilibrium. If the real frequency in a population varies from the predicted value, then it is an indicator of one or more assumptions being disrupted and violated, which can be further investigated. It also helps in predicting the prevalence of a negative recessive gene in the heterozygous carriers.

FAQs on Hardy Weinberg Law

1. Give the Assumptions of Hardy–Weinberg Equilibrium.

The following are the seven assumptions underlying the Hardy-Weinberg equilibrium:

  • organisms tend to be diploid

  • only sexual reproduction takes place

  • generations are found to be non-overlapping

  • mating tends to be random.

  • The population size is extremely large.

  • In all the sexes, allele frequencies are equivalent.

  • There occurs no gene flow, migration, admixture, selection or mutation.

2. Who else talked about genetic equilibrium?

Originally discovered independently by Wilhelm Weinberg along with  by Godfrey Harold Hardy.

3. How does mutation affect hardy weinberg?

In the gene sequence of DNA, mutations are irreversible changes. These modifications change genes and alleles that contribute to a population's genetic variation. While mutations cause changes in a population's genotype, they might or might not produce changes that are detectable or phenotypic. Specific genes or whole chromosomes could be affected by mutations. 


The lack of mutations in a population is among the conditions which must be fulfilled for the Hardy-Weinberg equilibrium. These modifications change genes and alleles that contribute to a population's genetic variation.