What is the Hardy-Weinberg principle?

The Hardy-Weinberg principle, also referred to together the Hardy-Weinberg equilibrium, is a set of 5 assumptions which once satisfied can enable the decision of allele and genotype frequencies that a population. This frequencies will additionally remain consistent for future generations. The principle was found by Godrey Hardy and Wilhelm Weinberg in 1908, based on Gregor Mendel’s law of Segregation. To estimate the frequency the alleles and genotypes that a specific population, over there is two simple formula that deserve to be used.

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The presumptions of the Hardy-Weinberg principle

There space 5 assumptions that space made when using the Hardy-Weinberg equations. These are:

No natural selection: There are no evolutionary pressures which may favour a certain allele.Random mating: each individual in a population mates randomly so the mating v an individual transferring a details allele is not favoured.No mutations: There are no DNA mutations occurring for the alleles which may affect their function.A close up door population: people within the populace do no leave and new individuals are not presented to the population.Large population size: The populace is considered big enough, at best infinite, so that significant changes in allele frequencies carry out not reason a genetic drift.

If any of these presumptions are no satisfied, then the principle cannot be applied.

Determining the allele frequency

The an initial Hardy-Weinberg equation (p + q = 1) pertains to estimating the frequency of alleles in a population. Each gene usually has actually two alleles (diploid organism), one from every parent. This alleles room denoted as the leading (A) and recessive (a) forms. These are stood for as ‘p‘ and also ‘q‘ is the equation below.

In a population, the an unified frequency that both the alleles have to equal 1 (100%).

Therefore, if the frequency of one allele is known, the is possible to calculation the frequency the the other allele simply by rearranging the equation.


In a population, there are two alleles for ear shape: having actually detached lobes (dominant, A) or having attached lobes (recessive, a). Determine the allele frequency of the recessive allele ‘a’ (attached lobes) provided the frequency of the dominant allele ‘A’ (attached lobes) is 73%.

1. To number this out we first need to fill in what us know into the Hardy-Weinberg equation, i.e. The allele ‘A‘ (p in the equation) frequency is 73% (which is the very same as 0.73).

2. Next, rearrange the formula to identify the worth of q (the recessive allele frequency). So this would give: q = 1 – 0.73.

3. Calculating this would mean: q = 0.27 (27%). So, 27% that the populace will have actually the allele because that attached earlobes.

The recessive allele frequency is 27%.

Determining the genotype frequencies

The Hardy-Weinberg equation supplied to determine genotype frequencies is: p2 + 2pq + q2 = 1.

Where ‘p2‘ represents the frequency the the homozygous dominant genotype (AA), ‘2pq‘ the frequency the the heterozygous genotype (Aa) and also ‘q2‘ the frequency the the homozygous recessive genotype (aa). The sum of these 3 genotypes should equal 1 (100%).

Again, if one genotype frequency is known, that is feasible to usage the Hardy-Weinberg equations to occupational out the others.


Let’s usage the same instance above concerning earlobes (detached lobes and also attached lobes). Identify the genotype frequency that the homozygous leading (AA) allele for having actually detached earlobes given the frequency of the fastened earlobe (aa) phenotype is 6%.

1. Through looking in ~ the question, we space asked to calculation (AA), for this reason ‘p2‘ in the Hardy-Weinberg equation, offered the frequency that aa (‘q2‘ in the equation) is 6% (we will occupational in decimal from this point, for this reason this would certainly be 0.06). Since ‘q2‘ equates to 0.06, we have the right to work out what ‘q‘ is through square-rooting 0.06. Act this provides 0.245.

2. Due to the fact that we now understand the allele frequency the the recessive allele (q), we deserve to use the an initial Hardy-Weinberg equation over (p + q = 1) to work-related out the allele frequency because that the leading allele (p).

3. We now recognize what p is (0.755). To calculation the genotype frequency the the homozygous leading genotype, we merely need to square the worth of p. Law this would provide 0.57. So, 57% the the population are homozygous dominant (AA). This would be the answer to our question.

The homozygous leading genotype frequency is 57%.

4. If you want to walk one action further and work the end the frequency that the heterozygous genotype (Aa), for this reason ‘2pq‘ in the Hardy-Weinberg equation, you deserve to do. Due to the fact that we know the worth of ‘p‘ (0.755) and ‘q‘ (0.245). All the is compelled is to main point 2 through 0.755 and also by 0.245. Doing this will provide 0.37. So, 37% the the population will have the heterozygous genotype (Aa).

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Notice, if you add all that the genotype frequencies together, this equates to 1 (0.57 + 0.37 + 0.06 = 1).