What is the idea of random drift?

• A. Random drift increases allele frequencies steadily
• B. Hardy-Weinberg assumes a large population where chance things average out. When dealing with small populations chance can have a dramatic effect.
• C. Random drift only occurs with mutation
• D. Random drift is the same as natural selection

Answer: (B)

Genetic drift is random fluctuation in allele frequencies from one generation to the next due to chance sampling effects. In large populations, these random changes tend to cancel out, so allele frequencies stay relatively stable and Hardy-Weinberg expectations hold. In small populations, however, just a few random events—who happens to reproduce, whose alleles get passed on—can cause big swings in allele frequencies. Over time this can lead to one allele becoming fixed or lost purely by chance, even without any selective advantage or new mutation. Drifts can move allele frequencies up or down randomly, not in a steady direction, so it isn’t the same as natural selection.