What describes a genetic bottleneck?

• A. Occurs when a population grows rapidly and expands genetic diversity.
• B. Occurs when a population is stabilized by natural selection.
• C. Occurs when a population is greatly reduced in size, limiting genetic diversity.
• D. Occurs when all individuals have identical genotypes.

Answer: (C)

A drastic drop in population size that leaves only a small number of individuals causes a genetic bottleneck, greatly reducing the genetic variation available for future generations. With so few survivors, genetic drift can rapidly fix or lose alleles, trimming the gene pool and lowering diversity. Even after the population recovers numerically, the surviving genetic material remains limited, which can reduce the ability to adapt to new environments or resist emerging diseases. This matches the idea of a population greatly reduced in size, limiting genetic diversity. The other scenarios describe growth with more diversity, stabilization by natural selection, or uniform genotypes, which do not reflect a bottleneck.