Identification: sex determination, chromatin: practice question

A Forensic Medicine 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.

Try it

Forensic Medicine · Identification: sex determination, chromatin

Sample item

A tall, phenotypically male adult has small firm testes, gynaecomastia and infertility. A buccal smear shows a Barr body in many nuclei. What is the likely karyotype?

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

The answer and the reasoning

B. 47,XXY

The number of Barr bodies equals the number of X chromosomes minus one. A male with one Barr body therefore has two X chromosomes, and the picture of tall stature, small testes and gynaecomastia indicates Klinefelter syndrome, 47,XXY. A chromatin-positive smear does not by itself prove female sex.

Option by option

  • A. 45,X

    45,X (Turner syndrome) gives a chromatin-negative smear and a female phenotype.

  • B. 47,XXY (correct)

    Correct. Two X chromosomes give one Barr body in a phenotypic male.

  • C. 47,XYY

    47,XYY has one X, so there is no Barr body.

  • D. 46,XY

    46,XY has one X and no Barr body.

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.

More Forensic Medicine questions

Questions about this Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is B, 47,XXY. The number of Barr bodies equals the number of X chromosomes minus one.

Why is "45,X" not the answer?

45,X (Turner syndrome) gives a chromatin-negative smear and a female phenotype.

Why is "47,XYY" not the answer?

47,XYY has one X, so there is no Barr body.

Why is "46,XY" not the answer?

46,XY has one X and no Barr body.

What concept does this question test?

It tests Identification: sex determination, chromatin in Forensic Medicine. A male with one Barr body therefore has two X chromosomes, and the picture of tall stature, small testes and gynaecomastia indicates Klinefelter syndrome, 47,XXY. A chromatin-positive smear does not by itself prove female sex.

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 Identification: sex determination, chromatin?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine 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.