Genetics: practice question

A Pediatrics 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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Pediatrics · Genetics

Sample item

A tall adolescent boy with long limbs, small firm testes, sparse body hair and gynaecomastia is being evaluated. What is the most likely karyotype?

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

The answer and the reasoning

A. 47,XXY

Tall stature, small firm testes, gynaecomastia and hypergonadotropic hypogonadism define Klinefelter syndrome. The karyotype is 47,XXY, usually due to non-disjunction, and testosterone replacement is given at puberty.

Option by option

  • A. 47,XXY (correct)

    Correct. An additional X chromosome in a male causes Klinefelter syndrome.

  • B. 47,XYY

    47,XYY males are tall but usually have normal testes and fertility.

  • C. 45,X

    45,X is Turner syndrome in a phenotypic female with short stature.

  • D. 47,XX with an extra chromosome 21

    An extra chromosome 21 produces Down syndrome with characteristic facies and hypotonia.

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 Pediatrics question

What is the answer to this Pediatrics question?

The best answer is A, 47,XXY. Tall stature, small firm testes, gynaecomastia and hypergonadotropic hypogonadism define Klinefelter syndrome.

Why is "47,XYY" not the answer?

47,XYY males are tall but usually have normal testes and fertility.

Why is "45,X" not the answer?

45,X is Turner syndrome in a phenotypic female with short stature.

Why is "47,XX with an extra chromosome 21" not the answer?

An extra chromosome 21 produces Down syndrome with characteristic facies and hypotonia.

What concept does this question test?

It tests Genetics in Pediatrics. The karyotype is 47,XXY, usually due to non-disjunction, and testosterone replacement is given at puberty.

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?

Memorise milestones and the vaccine schedule as tables and revise them often. Then use the flashcards and the other Pediatrics 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.