Question

Huntington's disease is caused by a single dominant allele and results in progressive mental and neurological damage. The disease usually becomes symptomatic when a person is between 30 and 50 years old and the patient usually dies within 15 years of diagnosis. Approximately 1 in 25,000 Caucasians have this disease. Huntington's disease has not been associated with any other disease, now or in the past. Why might natural selection not have eliminated such a deleterious allele from the population?

Select one:

A. Natural selection acts through reproduction, and most individuals with Huntington's disease reproduce prior to discovery.

B. Modern health care has acted as an agent against selection.

C. Diseases tend to remain in populations because of heterozygous carriers.

D. Natural selection only works on young individuals or newborns. Huntington's disease only works on older people.

E. Natural selection tends not to work on human diseases and in human populations.

Answer 1

The correct answer is option A- Natural selection acts through reproduction, and most individuals with Huntington's disease reproduce prior to discovery.

Explanation: As the disease is caused by a dominant allele , the carrier will also express the disease, so there should not be any carrier of this disease, heterozygotes also express the disease. Natural selection obviously acts on human disease and human populations and it works on every stage of life. But Natural selection operates through reproduction and as this disease is manifested at or after reproductive age, before onset of the disease, the allele spread to the next generation and hence it remains in the population. So Option a is correct.