Question

Under what circumstances might a lethal dominant allele persist in a population? Assume that a recessive autosomal disorder occurs in 1 of 10,000

Short answer

Answer: A lethal dominant allele can persist in a population through mechanisms such as incomplete penetrance, variable expressivity, late-onset disorder, and genetic drift. These conditions allow carriers of the lethal dominant allele to survive and reproduce, which helps to maintain the allele within the population.

Step-by-step solution

Review Dominant and Recessive Alleles

A dominant allele is one that expresses its phenotype even when there is only one copy present in an individual (heterozygous), while a recessive allele requires two copies in an individual (homozygous) to express its phenotype. In the context of this problem, the lethal dominant allele causes a serious disorder, while the presence of two copies of the recessive allele leads to the autosomal disorder.

Examine Incomplete Penetrance

Incomplete penetrance occurs when individuals carrying a lethal dominant allele do not always express the associated disorder. This allows the allele to persist in a population as it can be passed on to future generations without necessarily causing the disorder in each generation. In this case, the recessive autosomal disorder serves as a reference point for the prevalence.

Consider Variable Expressivity

Variable expressivity refers to the situation where individuals with the same genotype may express the phenotype to varying degrees. This can result in a range of severities of the disorder, which could allow carriers of the lethal dominant allele to survive and reproduce, passing the allele on to their offspring.

Look at Late-Onset Disorder

Late-onset disorder, in which the disorder does not present until later in life (e.g., Huntington's disease), can also contribute to the persistent presence of a lethal dominant allele in a population. Because the effects of the disorder do not manifest until after reproductive age, affected individuals can still reproduce and pass on the allele to their offspring.

Analyze Population Event like Genetic Drift

Genetic drift, which is random fluctuations in allele frequencies within a population, can also contribute to the persistence of a lethal dominant allele. If a population is small or experiences a population bottleneck, this could lead to an increase in the frequency of the lethal dominant allele.

Explain Under What Circumstances a Lethal Dominant Allele Might Persist

A lethal dominant allele can persist in a population through incomplete penetrance, variable expressivity, late-onset disorder, and genetic drift. The recessive autosomal disorder occurring at a frequency of 1 in 10,000 individuals can be considered as a reference point when examining these factors. In the presence of these conditions, carriers of the lethal dominant allele may survive and reproduce, allowing the allele to be maintained within the population.