Genetics: X-linked recessive pedigree: practice question

A Anatomy question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anatomy · Genetics: X-linked recessive pedigree

Sample item

A man with haemophilia A marries a woman with no family history and no carrier status. What is the genetic outcome for their children?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. All daughters are carriers and all sons are unaffected

Haemophilia A is X-linked recessive due to mutations in F8. A father gives his X chromosome to all his daughters, who become obligate carriers, and his Y chromosome to all his sons, who are unaffected. There is therefore no male-to-male transmission, a hallmark of X-linked inheritance.

Option by option

  • A. All daughters are carriers and all sons are unaffected (correct)

    Correct. Daughters receive the father's mutant X and sons receive his Y.

  • B. All sons are affected and all daughters are unaffected

    Sons receive the father's Y, not his X, so they cannot inherit an X-linked allele from him.

  • C. All daughters are affected and all sons are carriers

    Daughters would be affected only if they also received a mutant X from the mother, who is not a carrier.

  • D. Half the sons are affected and half the daughters are carriers

    This pattern applies when the mother is a carrier and the father is unaffected.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is A, All daughters are carriers and all sons are unaffected. Haemophilia A is X-linked recessive due to mutations in F8.

Why is "All sons are affected and all daughters are unaffected" not the answer?

Sons receive the father's Y, not his X, so they cannot inherit an X-linked allele from him.

Why is "All daughters are affected and all sons are carriers" not the answer?

Daughters would be affected only if they also received a mutant X from the mother, who is not a carrier.

Why is "Half the sons are affected and half the daughters are carriers" not the answer?

This pattern applies when the mother is a carrier and the father is unaffected.

What concept does this question test?

It tests Genetics: X-linked recessive pedigree in Anatomy. A father gives his X chromosome to all his daughters, who become obligate carriers, and his Y chromosome to all his sons, who are unaffected. There is therefore no male-to-male transmission, a hallmark of X-linked inheritance.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Genetics: X-linked recessive pedigree?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.