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?

The following qualities are assumed by the Hardy-Weinberg equilibrium:

(5) is immediately violated because a population cannot be confined to a small lake; it must be infinitely large.

(3) is likewise untrue; generations overlap because adulthood does not end when a person gives birth.

(7) is untrue. Although mutations are prohibited, trout have undergone mutations.

The previous point also probably disproves (4): sexual dimorphism is a trait shared by all species, meaning that trout with more advantageous traits (e.g., speed, strength, coloration) are more likely to mate. A mutation producing vibrant coloration will attract predators, and no trout would want to mate with another trout who is far more likely to be targeted by predators.

Regarding (1), mutations can result in differences in ploidy; most trout are diploid, but some can actually be triploid, despite the fact that this makes them infertile.

Some reasons the population of trout may not be at Hardy-Weinberg equilibrium include:

1. Mutation introducing new alleles.
2. Non-random mating, such as assortative mating based on color.
3. Genetic drift affecting allele frequencies due to the small population size.
4. Migration of trout into or out of the lake, altering allele frequencies.
5. Natural selection favoring certain traits, such as colorfulness, leading to differential survival and reproduction.