Population genetics (Hardy–Weinberg): Under which condition below are allele (gene) frequencies most likely to remain unchanged across generations?

Difficulty: Easy

Correct Answer: Random mating (panmixia) with other equilibrium assumptions

Explanation:


Introduction:
The Hardy–Weinberg principle outlines conditions under which allele and genotype frequencies remain constant from generation to generation. Recognizing which forces disturb equilibrium helps interpret real population data and design genetic studies.


Given Data / Assumptions:

  • Equilibrium requires: random mating, infinitely large population, no selection, no mutation, and no migration.
  • Any violation of these assumptions can shift allele frequencies.
  • The options listed represent common departures from equilibrium.


Concept / Approach:
Random mating (panmixia) is one of the necessary conditions for Hardy–Weinberg equilibrium. While random mating alone does not guarantee equilibrium if other assumptions are violated, it is the only option among those given that is compatible with stability of allele frequencies. The other options explicitly introduce forces (selection, drift via small size, migration, mutation) that change allele frequencies.


Step-by-Step Solution:

List Hardy–Weinberg assumptions: no selection, no mutation, no migration, large population, random mating.Evaluate each option for conformity or violation.Identify random mating as consistent with equilibrium, given other assumptions hold.Conclude that random mating best fits the condition for unchanging allele frequencies among the choices.


Verification / Alternative check:
Under random mating with all other assumptions satisfied, genotype frequencies stabilize at p^2, 2pq, q^2, and allele frequencies p and q remain constant across generations, confirming the principle.


Why Other Options Are Wrong:

  • Selection for homozygotes shifts allele frequencies toward favored alleles.
  • Small population size increases genetic drift, causing random fluctuations and fixation/loss.
  • Active migration introduces new alleles and changes frequencies.
  • Directional mutation changes allele proportions over time.


Common Pitfalls:
Thinking that random mating alone ensures equilibrium without considering the other assumptions; equilibrium is multifactorial, but among the listed options, it is the only compatible condition.


Final Answer:
Random mating (panmixia) with other equilibrium assumptions

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