Genetics: X-linked Hardy-Weinberg calculation: 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 Hardy-Weinberg calculation

Sample item

An X-linked recessive disorder affects 1 in 10,000 males in a population in Hardy-Weinberg equilibrium. What is the approximate frequency of carrier females?

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

The answer and the reasoning

D. 1 in 5,000

In males the disease frequency equals the allele frequency q, so q is 1 in 10,000. Carrier females have genotype frequency 2pq, which is about 2 x 0.0001 = 0.0002, or 1 in 5,000. Affected females have frequency q squared, which is 1 in 100,000,000, so females are almost always carriers rather than affected.

Option by option

  • A. 1 in 20,000

    1 in 20,000 results from halving 2q instead of doubling the allele frequency.

  • B. 1 in 10,000

    1 in 10,000 is the allele frequency, not the carrier frequency.

  • C. 1 in 100,000,000

    1 in 100,000,000 is q squared, the frequency of affected females.

  • D. 1 in 5,000 (correct)

    Correct. 2pq is about 2q = 2 in 10,000, or 1 in 5,000.

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 in 5,000. In males the disease frequency equals the allele frequency q, so q is 1 in 10,000.

Why is "1 in 20,000" not the answer?

1 in 20,000 results from halving 2q instead of doubling the allele frequency.

Why is "1 in 10,000" not the answer?

1 in 10,000 is the allele frequency, not the carrier frequency.

Why is "1 in 100,000,000" not the answer?

1 in 100,000,000 is q squared, the frequency of affected females.

What concept does this question test?

It tests Genetics: X-linked Hardy-Weinberg calculation in Anatomy. Carrier females have genotype frequency 2pq, which is about 2 x 0.0001 = 0.0002, or 1 in 5,000. Affected females have frequency q squared, which is 1 in 100,000,000, so females are almost always carriers rather than affected.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Hardy-Weinberg calculation?

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.