What is genetic drift effect during a bottleneck or founder event?

• A. Migration rate increases
• B. Population size is small
• C. Mutation rate increases
• D. Recombination increases

Answer: (B)

Genetic drift operates through random changes in allele frequencies, and its impact is strongest when the population is small. In a bottleneck, most individuals are wiped out, leaving only a limited number of survivors. In a founder event, a new population starts from just a few individuals. In both situations, the effective population size is greatly reduced, so random sampling of alleles from one generation to the next can cause big shifts in allele frequencies and a loss of genetic diversity simply by chance. That’s why the key factor here is that the population size is small.

The other options describe different concepts: migration rate relates to gene flow bringing in new alleles, mutation rate concerns the introduction of new variation, and recombination rate affects how alleles are shuffled during reproduction. While these processes matter in evolution, they are not what defines the immediate effect of a bottleneck or founder event—that effect is the increased influence of random drift due to the small population size.