Biology · Evolution · NEET
NCERT lists exactly five: (1) gene migration or gene flow, (2) genetic drift, (3) mutation, (4) genetic recombination, and (5) natural selection. Each one can change allele frequencies from one generation to the next. When frequencies change, the population is evolving, so a disturbed Hardy-Weinberg equilibrium is a sign of evolution.
Both change allele frequency when a part of a population moves. Gene flow (gene migration) is the DIRECTED movement of genes into or out of a population when migration happens repeatedly, so new alleles are added to the new population and lost from the old one. Genetic drift is the SAME kind of change but happening purely BY CHANCE, mostly in a small, isolated population. Rule: migration you can point to a cause; drift is random.
No. A constant gene pool is the CONDITION of equilibrium itself, not a factor that disturbs it. NEET 2024 asked exactly this. The five disturbing factors change the gene pool; a gene pool that stays constant means the population is AT equilibrium, so it cannot be a disturbing factor. This is the most common NTA trap.
Mutation creates brand-new alleles or changes one allele into another. This changes the allele frequencies (p and q) directly, so p and q no longer stay constant across generations. Since Hardy-Weinberg equilibrium requires no new mutations, any mutation breaks the equilibrium and contributes raw variation for evolution.
When a few individuals leave and start a new population, their allele frequencies may differ so much from the original that the new group becomes a new species. This is the founder effect, and it is caused by genetic drift (chance change in a small sample). NEET 2021 asked this directly and the answer is genetic drift.
Which of the following factors will not affect the Hardy-Weinberg equilibrium?
The factor that leads to Founder effect in a population is:
Genetic drift operates in
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Natural selection is the main directed force, because it changes allele frequencies in a specific direction (toward better-fit variants). The other four (gene flow, drift, mutation, recombination) supply or shuffle variation, but natural selection sorts it. All five together disturb Hardy-Weinberg equilibrium and drive evolution.
No. Any one of the five can disturb equilibrium on its own. In real populations several act at once, but for NEET you only need to know that the presence of ANY one of these five means the population is NOT at Hardy-Weinberg equilibrium.
Calculate expected allele frequencies (p and q) using p²+2pq+q²=1. If the measured frequency differs from the expected value, the difference and its direction show evolutionary change. A stable, unchanging frequency means no evolution; a changing frequency means one of the five factors is acting.
No. Mutation creates a new allele by changing the DNA. Genetic recombination reshuffles existing alleles into new combinations during meiosis (crossing over and independent assortment). Both are separate factors on the NCERT list of five.
