A population of trout lives in a small lake. Some of the trout have a mutation that makes them more colorful. What are some reasons this population is not at Hardy-Weinberg equilibrium?

1 Answer
Dec 21, 2015

The Hardy-Weinberg equilibrium assumes the following characteristics:

  1. organisms are diploid.
  2. only sexual reproduction occurs.
  3. generations are non overlapping.
  4. mating is random.
  5. population size is infinitely large.
  6. allele frequencies are equal in the sexes.
  7. there is no migration, mutation or selection.

(5) is immediately not met—a population must be infinitely large, not restricted to a small lake.

(3) is also false—the adult generation does not die as soon as they give birth, thus the generations overlap.

(7) is certainly not true. Mutations are not allowed, yet the trout have mutated.

The previous point also likely negates (4)—a mutation causing vibrant coloration will attract predators. Thus, no trout would want to mate with another trout who is far more likely to be targeted by predators. Additionally, sexual dimorphism is present in all species. This means that trout who have more favorable traits (e.g., speed, strength, coloration) are more likely to mate.

As for (1), mutations can cause variations in ploidy. Some trout actually can be triploid, even though it renders them infertile. However, most trout are diploid.