Which of the following does not affect the Hardy-Weinberg equilibrium?

The correct answer is Option (3) → Gene pool

Option (1) Natural selection — A factor that affects Hardy-Weinberg equilibrium. Individuals with useful variations survive and leave more offspring. Their alleles become more common in the next generation, so allele frequencies change.

Option (2) Genetic drift — A factor that affects Hardy-Weinberg equilibrium. Genetic drift is a change in allele frequency by chance. It is strongest in small populations. When a drifted group starts a new population, the effect is called the founder effect.

Option (3) Gene pool — Not a factor that affects Hardy-Weinberg equilibrium. The gene pool is the total of all the genes and their alleles in a population. It is not a force acting on the population. The Hardy-Weinberg principle says that the gene pool stays constant when nothing disturbs it. So the gene pool is what the factors change, not one of the factors.

Option (4) Gene migration — A factor that affects Hardy-Weinberg equilibrium. When a section of a population moves to another place, alleles are lost from the old population and added to the new one. Repeated migration of this kind is called gene flow.

NCERT Extract:
Hardy-Weinberg Principle – “… Five factors are known to affect Hardy-Weinberg equilibrium. These are gene migration or gene flow, genetic drift, mutation, genetic recombination and natural selection. When migration of a section of population to another place and population occurs, gene frequencies change in the original as well as in the new population.”