Final answer:
If a heterozygote has lower fitness than either homozygote, this situation is called underdominance. Underdominance is the opposite of heterozygote advantage, where heterozygous individuals have higher fitness and is associated with decreased genetic diversity.
Step-by-step explanation:
If a heterozygote has lower fitness than either homozygote, this is known as underdominance. Underdominance occurs when the presence of two different alleles (heterozygous condition) results in a reduced fitness of the individual compared to those with either of the homozygous genotypes. This situation discourages the presence of heterozygotes within the population and can lead to decreased genetic diversity.
In cases where a recessive trait is under consideration, the trait will be observed in individuals that are homozygous for that trait. Heterozygous individuals will not express the recessive trait if the dominant allele is present, as per Mendel's law of dominance.
Heterozygote advantage, on the other hand, is the opposite of underdominance. In heterozygote advantage, individuals with heterozygous alleles have higher fitness than both of the homozygous forms, which promotes genetic diversity in the population. Here, the value of 2pq, representing the frequency of heterozygotes in the population, would likely increase.
a