Which Is NOT an Assumption of the Hardy-Weinberg Model? Clarifying Key Population Genetics Concepts

The Hardy-Weinberg model is a fundamental framework in population genetics that predicts how allele and genotype frequencies remain constant from generation to generation in an idealized population. This model relies on several key assumptions to hold true. Understanding these assumptions is crucial for interpreting genetic data and identifying when evolutionary forces are at play.

The Core Assumptions of the Hardy-Weinberg Model

The Hardy-Weinberg equilibrium assumes:

1. Random mating: Individuals pair by chance without preference for genotype or phenotype.

2. No natural selection: All genotypes have equal chances of survival and reproduction.

3. No mutation: Alleles do not change from one form to another.

4. No gene flow: No migration of individuals or gametes into or out of the population.

5. Large (effectively infinite) population size: This prevents random fluctuations in allele frequencies (genetic drift).

6. Organisms are diploid and reproduce sexually.

7. Allele frequencies are equal in both sexes.

What About Dominance?

The dominance or recessiveness of alleles is not an assumption of the Hardy-Weinberg model. The model applies regardless of whether one allele is dominant, recessive, or if there is codominance or incomplete dominance. It predicts genotype frequencies based on allele frequencies alone, without requiring any specific dominance relationship.

Evaluating the Given Options

• (1) Population mates at random with respect to the locus in question: This is a fundamental assumption.

• (2) Selection is not acting on the locus in question: Also a key assumption to maintain equilibrium.

• (3) One allele is dominant and other is recessive at this locus: Not an assumption. Hardy-Weinberg equilibrium holds regardless of dominance.

• (4) The population is effectively infinite in size: Essential to avoid genetic drift.

Conclusion

The statement that one allele is dominant and the other is recessive at the locus is NOT an assumption of the Hardy-Weinberg model.

Correct answer: (3) One allele is dominant and other is recessive at this locus