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PCAT Biological Processes – Hardy-Weinberg Equilibrium

  • by Sam
  • Oct 24, 2017
  • PCAT Question of the Day

Which of the following theoretical populations would LEAST meet the requirements of the Hardy-Weinberg equilibrium?


A) A population small mammals with an infinite number of individuals in which there is no migration, generations overlap slightly, and mating is random

B) A population of large birds who only reproduce upon reaching 50 years of age, who mate for life, who only produce one offspring at a time, and who invest over five years in rearing each young before it leaves the next.

C) A population of newts consisting of a small number of individuals confined to a single cave that prevents migration, in which sexual selection prefers smaller males.

D) A population of gibbons living in a stable jungle ecosystem with a large number of randomly mating individuals, in which the allele frequencies are equal between sexes and from which a few individuals migrate each year.


The seven assumptions of the Hardy-Weinberg equilibrium are:

  1. Diploid organisms
  2. Sexual reproduction only
  3. Non-overlapping generations
  4. Random mating
  5. Infinite population size
  6. Equal allele frequencies between the sexes
  7. No evolution (i.e. no migration, mutation, or selection)

Comparing these assumptions to the answer choices, we see that (A) slightly violates one assumption, (B) is not explicitly stated to violate any assumptions, (C) violates two assumptions, and (D) slightly violates one assumption. Since choice (C) violates two assumptions, it is the least likely to fit the Hardy-Weinberg equilibrium and is thus the right answer.

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