Biology · Evolution · NEET
No. Natural selection is NON-random: the allele that gives higher Darwinian fitness (more surviving offspring) increases. Genetic drift is RANDOM: allele frequency changes by pure chance, not because one allele is better. Both are among the 5 factors that disturb Hardy-Weinberg equilibrium, but only selection is guided by fitness. NEET often puts them together as options to test this exact difference.
In a small sample, chance events (like a few individuals dying or not mating) can change allele frequency a lot. In a very large population these chance changes average out and cancel each other, so the frequency stays almost the same. This is why NCERT states genetic drift operates in a small, isolated population. If you toss a coin 4 times you may get 4 heads by chance; toss it 4000 times and you get close to 50-50.
The founder effect is caused by genetic drift. A small group leaves the original population and starts a new one; the allele frequencies of this small founder group differ by chance from the parent population. NCERT and NEET 2021 both state: the factor that leads to the founder effect is genetic drift. Gene flow (gene migration) is a separate factor where genes move BETWEEN populations.
Yes, NCERT says so. Sometimes the change in allele frequency in the new sample is so different that the drifted group becomes a different species. The original drifted population becomes the founders, and this is the founder effect. So drift, through the founder effect, can lead to speciation without natural selection acting.
Both are forms of genetic drift acting on a small group. Founder effect: a FEW individuals migrate and start a NEW population with a chance-different gene pool. Bottleneck effect: a large population is suddenly REDUCED (disaster, disease) so the few survivors carry a chance-different gene pool. NEET syllabus mainly names the founder effect, but knowing both prevents confusion in assertion-reason questions.
No. Genetic drift is random; it does not care whether an allele is beneficial, harmful, or neutral. A harmful allele can even increase, and a good allele can be lost, purely by chance in a small population. This is the key point that separates drift from natural selection in NEET options.
Genetic drift operates in
The factor that leads to Founder effect in a population is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. The 5 factors that disturb Hardy-Weinberg equilibrium are gene migration (gene flow), genetic drift, mutation, genetic recombination and natural selection. Genetic drift changes allele frequency by chance, so it breaks the equilibrium.
Genetic drift is completely random. It changes allele frequency by chance, with no regard to whether an allele is good or bad. Only natural selection is directional and based on fitness.
The founder effect is genetic drift that happens when a few individuals leave and start a new population whose allele frequencies differ by chance from the original population.
Yes. NCERT states that sometimes the drifted new sample is so different in allele frequency that it becomes a different species, with the drifted group acting as founders.
In a large population, chance changes in different directions cancel out and average away, so allele frequency stays almost constant. Chance effects dominate only in small populations.
