What is the bottleneck effect and what consequence can it have on evolution?

What is the bottleneck effect and what consequence can it have on evolution?

• A. A gradual change in allele frequencies due to migration.
• B. A stable population maintains genetic variation.
• C. A sharp reduction in population size due to disaster, causing random changes in allele frequencies and loss of variation.
• D. A process that increases genetic differences between populations.

Answer: (C)

The bottleneck effect arises when a disaster or other event sharply reduces a population’s size, so only a small, random sample of the original gene pool remains. With so few individuals, genetic drift dominates and allele frequencies can change by chance from one generation to the next, leading to the loss of genetic variation as some alleles disappear entirely. This reduction in diversity matters for evolution because it limits the raw material available for natural selection to act on; the population may struggle to adapt to new environments or stresses. Even after numbers recover, the genetic makeup reflects those survivors, and reduced variation can persist unless new variation is introduced by mutation or migration. This phenomenon is not about gene flow, nor about a stable population maintaining variation, nor about processes that steadily increase differences between populations.

The bottleneck effect arises when a disaster or other event sharply reduces a population’s size, so only a small, random sample of the original gene pool remains. With so few individuals, genetic drift dominates and allele frequencies can change by chance from one generation to the next, leading to the loss of genetic variation as some alleles disappear entirely. This reduction in diversity matters for evolution because it limits the raw material available for natural selection to act on; the population may struggle to adapt to new environments or stresses. Even after numbers recover, the genetic makeup reflects those survivors, and reduced variation can persist unless new variation is introduced by mutation or migration. This phenomenon is not about gene flow, nor about a stable population maintaining variation, nor about processes that steadily increase differences between populations.