In mutation-drift balance, drift causes random fluctuations; mutation introduces new alleles at rate μ, creating a balance over time.

• A. Drift fixes alleles while mutation reduces variation.
• B. Mutation immediately eliminates drift.
• C. Drift causes random fluctuations; mutation introduces new alleles at rate μ, creating a balance with drift over time.
• D. Mutation has no effect on drift balance.

Answer: (C)