A genetic counselor is consulted by a young man who is worried about developing Huntington’s disease, an inherited disorder caused by a dominant allele of a single gene. The young man explains that his cousin was recently diagnosed with Huntington’s disease, and the news has caused him to consider his own risk of developing the disorder. Which of the following questions will best help the genetic counselor to evaluate the risk of the young man developing Huntington’s disease and transmitting it to his children?

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The question asks which line of questioning will best help a genetic counselor assess both the young man’s own risk of developing Huntington’s disease and the risk of transmitting it to his children.

Option: "Were your parents or grandparents ever diagnosed with Huntington’s disease?" This is a strategically strong question because Huntington’s disease is inherited in an autosomal dominant pattern. Knowing whether close relatives (especially parents or grandpar­ents) have been diagnosed helps determine whether the affected allele is present in the family line, which directly informs the man’s own risk (and the risk to his offspring). If a parent is affected, the man has a 50% chance of having inherited the disease allele and thus a 50% chance of transmitting it to each child. If no first- or second-degree relatives are affected, the likelihood decreases, though it does not entirely eliminate risk due to possibilities like de novo mutations being extremely rare for this condition, or undisclosed/unknown family history.

Why this line of questioning is preferable: it targets the core genetic mechanism (dominant inheritance) and uses family history as a practical and efficient way to estimate risk, which is precisely what a genetic counselor aims to determine.

Why other approaches would be less informative (hypothetical, since no other options are listed): questions that focus on unrelated symptoms, environmental factors, or unrelated disorders would not address the inherited risk pattern of Huntington’s disease. They would fail to leverage the key information that pedigree and familial diagnosis provide about penetrance and transmission risk.

In summary, asking about whether parents or grandparents were diagnosed with Huntington’s disease directly informs both the probability that the man carries the dominant allele and the likelihood that he could pass it to his children, making it the most informative initial question in this scenario.

APBIO141-031 with labs S14 - CollegeBoard* AP Exam Prep: Multiple Choice

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