Medical genetics: recombination: 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 · Medical genetics: recombination

Sample item

Genetic recombination between homologous chromosomes depends on crossing over. During which phase of meiosis does crossing over take place?

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

The answer and the reasoning

A. Pachytene of prophase I

Homologous chromosomes are paired in synapsis at pachytene, and crossing over exchanges segments between non-sister chromatids. The resulting chiasmata become visible later at diplotene.

Option by option

  • A. Pachytene of prophase I (correct)

    Correct. Crossing over occurs between synapsed homologues at pachytene.

  • B. Interphase before meiosis I

    Interphase replicates DNA, but homologues are not paired for exchange then.

  • C. Metaphase I

    Metaphase I lines up the bivalents but crossing over has already happened.

  • D. Anaphase II

    Anaphase II separates sister chromatids and does not exchange material.

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, Pachytene of prophase I. Homologous chromosomes are paired in synapsis at pachytene, and crossing over exchanges segments between non-sister chromatids.

Why is "Interphase before meiosis I" not the answer?

Interphase replicates DNA, but homologues are not paired for exchange then.

Why is "Metaphase I" not the answer?

Metaphase I lines up the bivalents but crossing over has already happened.

Why is "Anaphase II" not the answer?

Anaphase II separates sister chromatids and does not exchange material.

What concept does this question test?

It tests Medical genetics: recombination in Anatomy. The resulting chiasmata become visible later at diplotene.

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 Medical genetics: recombination?

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.