The Hardy-Weinberg Law

If there is no selective pressure imposed on a
pair of alleles, one dominant the other recessive, their frequencies
should remain constant. This is known as **genetic
equilibrium**.

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The Hardy-Weinberg Law states:

both gene and genotype frequencies will remain unchanged -- in equilibrium -- unless outside forces change those frequencies.

**How the Hardy-Weinberg Law
works.**

When only 2 alleles (A, a) are involved, the relative proportions -- that is the frequencies of A & a -- must equal 1.If in a population where 80% of the alleles of the gene under study are allele A, the frequencies will be: A= 0.8 and a = 1- 0.8 = 0.2

Mathematically the Hardy Weinberg law is stated as:

A^{2} + 2Aa + a^{2} =
1

using the information above we can find the frequencies of the homozygous and heterozygous genotypes;

SO:

AA = (.8)^{2} = .64

2Aa = 2(.8 x .2) =.32

aa = (.2)^{2} = .04

The modified Punnett square would be:

If we can identify the individuals in a population that are homozygous for a particular allele of interest we can then calculate the frequency of that allele. If for instance 1/10,000 babies are born with a certain recessive genetic defect we can easily determine the allele frequencies of A & a

**a =
= 0.01 **

**therefore A=.99**

Conditions Necessary for the Hardy-Weinberg Law

In order for allele frequencies to remain unchanged (i.e. no evolution) the following restrictions must hold:

- Mating must be completely random
- There can be no mutations
- Gene flow must not occur (no migration)
- The population in question must be very large (infinite in size)
- The alleles must segregate according to Mendel's first law
- There can be no selection on the population

- Cystic Fibrosis - An example of the Hardy-Weinberg Law
- What's Hardy-Weinberg Law - In Japanese
- The Hardy-Weinberg Law -Kimball
- Hardy Weinberg Equilibrium Model
- Hardy Weinberg Equilibrum
- Hardy Weinberg Equation

Page updated March 7, 2003