[Campbell Biology P.541] A small, isolated population of an endangered bird species experien... | Practice Question

A small, isolated population of an endangered bird species experiences a sudden disease outbreak, significantly reducing its numbers. This event leads to a change in the allele frequencies for several genes, not due to selection, but purely by chance. Based on the Hardy-Weinberg equilibrium conditions, which condition is primarily violated, and what is the evolutionary mechanism at play?

  • A: No mutations; The gene pool is modified if new alleles are introduced.
  • B: Random mating; Genotype frequencies change due to non-random mating.
  • C: Extremely large population size; Allele frequencies fluctuate by chance (genetic drift).
  • D: No natural selection; Allele frequencies change when individuals with different genotypes have different survival or reproductive success.

Explanation

The scenario describes a 'bottleneck event' where a small population experiences a drastic reduction in numbers, leading to allele frequency changes 'by chance'. This directly violates the condition of 'extremely large population size' and is a classic example of genetic drift, specifically the bottleneck effect.