Genetics: mitochondrial inheritance: 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: mitochondrial inheritance

Sample item

A man has a pathogenic mitochondrial DNA point mutation that causes MELAS. His wife is unaffected and has no mutation. What is the risk that their children inherit the mutation?

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

The answer and the reasoning

B. Practically none, since mitochondria come from the oocyte

Mitochondrial DNA is inherited maternally, because the mitochondria of the sperm are degraded after fertilisation. An affected father does not transmit the mutation, whereas an affected mother transmits it to all children, with variable severity because of heteroplasmy and the bottleneck in oogenesis.

Option by option

  • A. 100% of daughters only

    Transmission to daughters only would suggest X-linked dominant with male-to-female transmission, not mitochondrial.

  • B. Practically none, since mitochondria come from the oocyte (correct)

    Correct. Paternal mitochondria do not contribute to the zygote, so there is essentially no risk.

  • C. 50% of sons only

    Sex-limited transmission to sons would suggest Y-linked inheritance, not mitochondrial.

  • D. 25% of all children

    A 25% risk is the expected figure for autosomal recessive carrier matings.

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 B, Practically none, since mitochondria come from the oocyte. Mitochondrial DNA is inherited maternally, because the mitochondria of the sperm are degraded after fertilisation.

Why is "100% of daughters only" not the answer?

Transmission to daughters only would suggest X-linked dominant with male-to-female transmission, not mitochondrial.

Why is "50% of sons only" not the answer?

Sex-limited transmission to sons would suggest Y-linked inheritance, not mitochondrial.

Why is "25% of all children" not the answer?

A 25% risk is the expected figure for autosomal recessive carrier matings.

What concept does this question test?

It tests Genetics: mitochondrial inheritance in Anatomy. An affected father does not transmit the mutation, whereas an affected mother transmits it to all children, with variable severity because of heteroplasmy and the bottleneck in oogenesis.

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: mitochondrial inheritance?

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.