Genetics: consanguinity: 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: consanguinity

Sample item

In a community where first-cousin marriages are common, a couple who are first cousins ask about risk to their child. What is the coefficient of inbreeding of their child?

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

The answer and the reasoning

D. 1/16

First cousins share one-eighth of their genes, and the chance that their child inherits two copies of the same ancestral allele at a locus is half of that, or 1/16. This is the inbreeding coefficient, and it raises the risk of autosomal recessive disease in the offspring.

Option by option

  • A. 1/8

    1/8 is the proportion of genes shared by the cousins themselves, not the child's inbreeding coefficient.

  • B. 1/32

    1/32 applies to the child of first cousins once removed.

  • C. 1/4

    1/4 is the proportion of genes shared by half-siblings or by uncle and niece, and is not the coefficient for this child.

  • D. 1/16 (correct)

    Correct. The inbreeding coefficient for a child of first cousins is 1/16.

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 D, 1/16. First cousins share one-eighth of their genes, and the chance that their child inherits two copies of the same ancestral allele at a locus is half of that, or 1/16.

Why is "1/8" not the answer?

1/8 is the proportion of genes shared by the cousins themselves, not the child's inbreeding coefficient.

Why is "1/32" not the answer?

1/32 applies to the child of first cousins once removed.

Why is "1/4" not the answer?

1/4 is the proportion of genes shared by half-siblings or by uncle and niece, and is not the coefficient for this child.

What concept does this question test?

It tests Genetics: consanguinity in Anatomy. This is the inbreeding coefficient, and it raises the risk of autosomal recessive disease in the offspring.

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: consanguinity?

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.