Under what circumstances might a lethal dominant allele persist in a population?

Verified step by step guidance

1. Understand what a lethal dominant allele is: it is an allele that causes death when present in just one copy (heterozygous or homozygous state), typically preventing individuals from reproducing.
2. Consider that for a lethal dominant allele to persist, it must be passed on before the lethal effect occurs, meaning the allele's harmful effect happens after the individual has reproduced (late onset).
3. Recognize that if the lethal effect occurs after reproductive age, individuals can still pass the allele to offspring, allowing the allele to remain in the gene pool.
4. Another circumstance is if the allele has incomplete penetrance or variable expressivity, meaning not all individuals with the allele show the lethal phenotype, so some carriers survive and reproduce.
5. Also, new mutations can introduce the lethal dominant allele into the population continuously, balancing the loss of individuals who die from the allele.

Key Concepts

Lethal Dominant Alleles

A lethal dominant allele causes death when present in just one copy, often before reproductive age. Such alleles typically reduce an individual's fitness drastically, making their persistence in a population unusual unless specific conditions allow carriers to reproduce.

Heterozygote Advantage and Delayed Onset

Lethal dominant alleles may persist if their harmful effects appear after reproductive age, allowing carriers to pass the allele to offspring. Additionally, if heterozygotes have some survival or reproductive advantage, the allele can be maintained despite its lethality.

Mutation-Selection Balance

New lethal dominant alleles can continuously arise through mutation, balancing their removal by natural selection. This mutation-selection balance can maintain the allele at low frequencies in the population despite its negative effects.