Question

Huntington's disease is caused by a single dominant allele. It is a lethal disease, yet it persists in the human population. Which of the following statements best describes why?

1) The disease only affects individuals after they have already reproduced.
2) The disease provides a selective advantage in certain environments.
3) The disease is caused by a recessive allele that is not lethal.
4) The disease is caused by a mutation that is not inherited.

Answer 1

Huntington's disease persists in the population because the onset usually occurs after affected individuals have reached reproductive age, allowing them to pass on the dominant allele to their offspring before symptoms manifest.

Step-by-step explanation:

Huntington's disease is a condition caused by a single dominant allele that leads to lethal autosomal dominant disorders. Despite its lethal nature, the disease persists in human populations because its symptoms generally do not manifest until after the affected individuals have reached reproductive age and possibly passed the defective allele to their offspring.

People who are heterozygous for the dominant Huntington allele (Hh) will develop Huntington's disease typically around middle age, after they might have already reproduced. Since the expression of the disease typically occurs after the childbearing years, the faulty gene can be transmitted to the next generation. This delayed onset allows the disease allele to be maintained in the population despite its lethal outcome.