Q.State the Hardy-Weinberg's law.

Hardy–Weinberg law: in a large, random-mating population free of mutation, migration, drift and selection, allele and genotype frequencies stay constant, and p² + 2pq + q² = 1.

The Hardy–Weinberg principle is the foundation of population genetics. It describes an idealised, non-evolving population — a reference against which real, evolving populations are compared.

Statement: In a large population that mates at random, the frequencies of alleles and of genotypes remain constant (in genetic equilibrium) from one generation to the next, as long as certain conditions are met.

The conditions (no evolutionary force acting):

1. No mutation.
2. No gene flow / migration (no genes entering or leaving).
3. No genetic drift (population is very large, so no random change).
4. Random mating (no assortative or selective mating).
5. No natural selection (all genotypes equally fit).

Mathematical expression: if a gene has two alleles with frequencies p and q, then p + q = 1, and the genotype frequencies are given by the binomial expansion:

p² (homozygous dominant) + 2pq (heterozygous) + q² (homozygous recessive) = 1.

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