5 Genetics and Evolution
5.7 Hardy-Weinberg principle
5.7 Hardy-Weinberg principle
Dr V Malathi
The Hardy-Weinberg Law, also known as the Hardy-Weinberg Principle or Hardy-Weinberg Equilibrium was formulated byG.H. Hardy, a British mathematician, and Wilhelm Weinberg, a German physician, in 1908.
It is a foundational concept in population genetics providing a mathematical framework for understanding how gene frequencies in a population remain constant over generations under certain conditions.
The Hardy–Weinberg principle/ law, states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.
This condition is called genetic equilibrium.
Key Assumptions of the Hardy-Weinberg Equilibrium
The Hardy-Weinberg equilibrium is based on a set of ideal conditions:
- Large Population Size: Genetic drift (random changes in allele frequencies) is minimal in large populations.
- Random Mating: Individuals pair by chance, not according to genotype or phenotype.
- No Mutation: No new alleles are introduced or altered.
- No Migration: No new members enter or leave the population, keeping allele frequencies stable.
- No Natural Selection: All genotypes have equal chances of surviving and reproducing.
The Hardy-Weinberg Equation
The Hardy-Weinberg equation is used to predict the genetic variation in a population under these ideal conditions.
Let us assume that there are two alleles for a particular gene in a population, typically represented by:
- p (frequency of the dominant allele, Y)
- q (frequency of the recessive allele, y)
Then: According to Hardy-Weinberg equation the sum of the allele frequencies must equal 1
i.e., p + q = 1
Using these allele frequencies, we can predict the genotype frequencies in the population with the formula:
where:
- p² = frequency of individuals with the homozygous dominant genotype (YY)
- 2pq = frequency of individuals with the heterozygous genotype (Yy)
- q² = frequency of individuals with the homozygous recessive genotype (yy)
Example of the Hardy-Weinberg Principle
Suppose in a population, 80% of alleles for a certain gene are dominant (A), and 20% are recessive (a):
- p = 0.8
- q = 0.2
Using the Hardy-Weinberg equation:
- p² = (0.8)² = 0.64 (64% are AA)
- 2pq = 2 * 0.8 * 0.2 = 0.32 (32% are Aa)
- q² = (0.2)² = 0.04 (4% are aa)
This means that in this ideal population, 64% would be homozygous dominant, 32% heterozygous, and 4% homozygous recessive.
while no population can satisfy those conditions, the principle offers a useful model against which to compare real population changes.
“Hardy-Weinberg Principle of Equilibrium” by Libre Texts Biology is licensed under CC BY 4.0