- A A slow, gradual reduction in overall population size that unfolds steadily across many successive generations, rather than a sudden, catastrophic population crash triggered abruptly by disease or habitat loss events as widely reported in standard practice under most conditions encountered
- B Drastic reduction in population size due to a catastrophic event (earthquake, disease, hunting); surviving population has reduced genetic diversity; subsequent evolution influenced by this reduced gene pool; example: cheetah (near extinction ~10,000 years ago, all nearly genetically identical)
- C The cumulative effect that ongoing migration between neighboring populations has on shared allele frequencies over time, a process of allele sharing through interbreeding rather than one driven by survivors of a crash event as frequently observed in practice in many documented cases according to conventional understanding
- D The cumulative effect that an elevated mutation rate has specifically within very small, isolated populations, attributing reduced genetic diversity to new mutation input rather than to the loss of surviving lineages over time in routine practice overall in most cases under typical conditions
Correct answer: B. Drastic reduction in population size due to a catastrophic event (earthquake, disease, hunting); surviving population has reduced genetic diversity; subsequent evolution influenced by this reduced gene pool; example: cheetah (near extinction ~10,000 years ago, all nearly genetically identical)
Explanation: Bottleneck effect: population crash → small surviving population has reduced genetic diversity (many alleles lost by chance). Different from founder effect: entire population reduced, not a new colony. Examples: (1) Northern elephant seals - hunted to ~20 individuals in 19th century, very low genetic diversity; (2) Cheetah - genomic studies show near-complete loss of diversity from ancient bottleneck; (3) Human population - genetic evidence of bottleneck ~70,000 years ago (Toba supervolcano?).
Concept context
Origin of life, Darwin's theory, natural selection, speciation, and evidence for evolution.