Which is the most powerful force for changing gene frequency in the short term?

Which is the most powerful force for changing gene frequency in the short term?

• A. Mutation
• B. Migration
• C. Natural selection
• D. Genetic drift

Answer: (D)

Genetic drift is the random change in allele frequencies that happens because you’re sampling a finite set of individuals each generation. In the short term, especially in small populations, this sampling error can cause large, unpredictable shifts from one generation to the next, independent of any fitness differences. So alleles can rise to high frequency or be lost purely by chance, making drift the most powerful force for changing gene frequencies over a short timescale when population size is small. Mutation introduces new alleles but at very low rates, migration changes frequencies gradually unless there's a huge influx, and natural selection requires a fitness difference to push frequencies—whereas drift can move frequencies sharply without any selection. The impact of drift is stronger in smaller populations because the random sampling effect is larger when there are fewer breeding individuals.

Genetic drift is the random change in allele frequencies that happens because you’re sampling a finite set of individuals each generation. In the short term, especially in small populations, this sampling error can cause large, unpredictable shifts from one generation to the next, independent of any fitness differences. So alleles can rise to high frequency or be lost purely by chance, making drift the most powerful force for changing gene frequencies over a short timescale when population size is small. Mutation introduces new alleles but at very low rates, migration changes frequencies gradually unless there's a huge influx, and natural selection requires a fitness difference to push frequencies—whereas drift can move frequencies sharply without any selection. The impact of drift is stronger in smaller populations because the random sampling effect is larger when there are fewer breeding individuals.