Which statement best describes genetic drift in small populations?

Which statement best describes genetic drift in small populations?

• A. Mutations are the only source of new alleles affecting allele frequencies.
• B. Natural selection is the primary cause of random allele frequency changes in small populations.
• C. Genetic drift causes random fluctuations in allele frequencies, especially in small populations; founder effect and bottleneck are two scenarios.
• D. Gene flow reduces genetic variation within a population.

Answer: (C)

Genetic drift is the random change in allele frequencies from one generation to the next due to sampling effects when organisms reproduce, and it matters most in small populations. In small groups, chance events can cause certain alleles to become more common or disappear entirely simply by luck, and over time this can lead to some alleles becoming fixed while others are lost, independent of any fitness advantage. The founder effect and bottlenecks are classic scenarios that illustrate how drift can strongly shape genetic variation in small populations. The other statements don’t capture this random, size-dependent process: mutations aren’t the sole source of allele variation and drift is not driven by selection, which is non-random. Gene flow tends to introduce new alleles from other populations and often increases genetic variation within a population, while reducing differences between populations.

Genetic drift is the random change in allele frequencies from one generation to the next due to sampling effects when organisms reproduce, and it matters most in small populations. In small groups, chance events can cause certain alleles to become more common or disappear entirely simply by luck, and over time this can lead to some alleles becoming fixed while others are lost, independent of any fitness advantage. The founder effect and bottlenecks are classic scenarios that illustrate how drift can strongly shape genetic variation in small populations. The other statements don’t capture this random, size-dependent process: mutations aren’t the sole source of allele variation and drift is not driven by selection, which is non-random. Gene flow tends to introduce new alleles from other populations and often increases genetic variation within a population, while reducing differences between populations.