Final answer:
Option a) Huntington's disease remains in the population because it typically manifests after individuals have had children, allowing them to pass the dominant allele responsible for the disease to their offspring. This late onset is a key reason why Huntington's, a genetic disease with autosomal dominant inheritance, persists across generations.
Step-by-step explanation:
Huntington's disease is an autosomal dominant disorder. This means that the presence of just one faulty dominant allele results in the expression of the disease. However, the symptoms of Huntington's disease typically do not appear until middle age, often after individuals have had children, allowing them to pass on the dominant allele to the next generation.
A correct answer to the student's question is that the illness strikes in adulthood, generally after affected individuals have produced offspring. Thus, the affected individuals may have already passed the allele to approximately 50 percent of their offspring before the onset of the disease. Genetic counseling can help individuals with a family history of Huntington's disease understand their risks and options, including genetic testing.
Though some genetic diseases manifest earlier in life, the late onset of Huntington's disease allows it to remain in the population, as those who carry the gene might unknowingly pass it to their children before symptoms develop.