Question

The allele that causes Huntington disease in humans is an example of a(n) _______ that exerts its effects later in life?

1) Dominant allele
2) Recessive allele
3) Codominant allele
4) Polygenic allele

Answer 1

The allele responsible for Huntington's disease is a dominant lethal allele that usually manifests in middle age, after reproduction has occurred, allowing the allele to be inherited by the next generation.

Step-by-step explanation:

The allele that causes Huntington's disease in humans is an example of a dominant lethal allele that exerts its effects later in life. This genetic condition is characterized by the gradual degeneration of the nervous system, with symptoms typically appearing in middle age, often after the individual has reproduced.

Huntington's disease is an autosomal dominant disorder, meaning only one copy of the mutant allele is necessary for an individual to express the disease. The mutant allele results in a protein with abnormal repeats of the amino acid glutamine which is toxic to neural tissue and leads to the disease's progressive symptoms like impaired motor function and personality changes. Since Huntington's disease may not manifest until the person is well into adulthood, it is possible for the allele to be passed onto offspring before it is diagnosed. Therefore, despite being lethal, the allele remains in the population, and individuals with a family history of Huntington's are often provided with genetic counseling.