Which response demonstrates the most accurate understanding of genetic drift?

• A. It is more likely to happen in a large population, because the population has more alleles to be lost
• B. It is more likely to happen in a large population, because more offspring are produced than in a small population
• C. It is more likely to happen in a small population, because the members of the small population are not as healthy as are the members of the large population
• D. It is more likely to happen in a small population, because random events can have a greater effect on allele frequencies in a small population than in a large population

Answer: (D)

Genetic drift is random fluctuations in allele frequencies from one generation to the next, driven by chance sampling rather than by natural selection. In a small population, these random events can have a large impact because the sample of alleles passed to the next generation represents a bigger fraction of the gene pool; a few luckier or unluckier individuals can shift frequencies dramatically, potentially causing alleles to become fixed or lost and reducing genetic variation. In contrast, large populations average out these random effects, so allele frequencies change more slowly and drift is weaker. The statement that drift is more likely in a small population because random events can have a greater effect on allele frequencies captures this idea. The other options either link drift to factors like the total number of offspring or health, which aren’t what drives drift, or imply that drift is more likely in larger populations, which is not correct.