Hardy-Weinberg Principle
ஹார்டி-வெய்ன்பெர்க் கொள்கை
Evolution is not random chaos; it is a mathematical certainty. If you think allele frequencies change by accident, you have already lost marks. Hardy-Weinberg is the baseline against which all evolutionary change is measured.
The idea
The Hardy-Weinberg principle states that allele frequencies in a population remain constant from generation to generation, maintaining genetic equilibrium. The sum of all allelic frequencies is 1. The equation p² + 2pq + q² = 1 represents the distribution of genotypes, where p and q are the frequencies of dominant and recessive alleles respectively.
Why it matters
It serves as a mathematical null hypothesis to measure evolutionary change; when frequencies deviate, it indicates that evolution is occurring due to specific factors.
NEET lens
NEET expects you to solve for p or q given the frequency of recessive individuals (q²). Remember the five factors that disturb equilibrium: gene migration, genetic drift, mutation, genetic recombination, and natural selection. Do not confuse p² with p; always take the square root to find the allele frequency. This is a high-yield calculation topic.
Clinical significance
When genetic equilibrium is disrupted, natural selection or genetic drift occurs, leading to the accumulation of deleterious mutations. In humans, this is observed in the high frequency of specific recessive disorders like Sickle-cell anemia in populations where malaria is endemic. Equilibrium failure is the precursor to evolutionary divergence and disease susceptibility.
Introduction
The Hardy-Weinberg principle states that allele frequencies in a population are stable and constant from generation to generation — genetic equilibrium — unless some factor disturbs them.
Core concept
Equation: for two alleles with frequencies p and q, p + q = 1 and p² + 2pq + q² = 1, where p² = frequency of AA, 2pq = Aa and q² = aa. The gene pool (total genes and their alleles) remains constant. Five factors disturb the equilibrium: gene migration (gene flow), genetic drift, mutation, genetic recombination during gametogenesis, and natural selection. When frequency change is by chance, it is genetic drift; if the change is so large that a new population forms, the original drifted population becomes the founders — the founder effect.
Go deeper
A disturbance in genetic equilibrium (change in allele frequency) is interpreted as evolution. So Hardy-Weinberg gives a 'null model' against which evolution can be measured.
From Class 10
If nothing changes in a population — no new genes coming in, no selection — the proportion of each gene variant stays the same. That steady state is Hardy-Weinberg equilibrium.