General physiology: mitochondrial inheritance: practice question

A Physiology 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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Physiology · General physiology: mitochondrial inheritance

Sample item

A mother with lactic acidosis, stroke-like episodes and myopathy passes the disease to all her children, whereas an affected father in another family passes it to none. Which feature of the zygote best explains this pattern?

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

The answer and the reasoning

B. Mitochondria are inherited almost exclusively from the oocyte

The zygote inherits its mitochondria and mitochondrial DNA essentially from the oocyte cytoplasm, because paternal mitochondria are diluted or eliminated after fertilisation. Mitochondrial disease therefore passes from affected mothers to all offspring and not from affected fathers.

Option by option

  • A. Mitochondrial DNA is completely absent from sperm

    Sperm mitochondria exist but are eliminated after fertilisation, so saying they are absent is inaccurate.

  • B. Mitochondria are inherited almost exclusively from the oocyte (correct)

    Correct. The oocyte supplies essentially all the zygote's mitochondria.

  • C. The trait is carried on a Y chromosome gene

    A Y-linked trait would pass only from father to son.

  • D. The affected gene lies on the X chromosome

    X-linked traits pass from fathers to daughters, which does not fit this pattern.

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 Physiology question

What is the answer to this Physiology question?

The best answer is B, Mitochondria are inherited almost exclusively from the oocyte. The zygote inherits its mitochondria and mitochondrial DNA essentially from the oocyte cytoplasm, because paternal mitochondria are diluted or eliminated after fertilisation.

Why is "Mitochondrial DNA is completely absent from sperm" not the answer?

Sperm mitochondria exist but are eliminated after fertilisation, so saying they are absent is inaccurate.

Why is "The trait is carried on a Y chromosome gene" not the answer?

A Y-linked trait would pass only from father to son.

Why is "The affected gene lies on the X chromosome" not the answer?

X-linked traits pass from fathers to daughters, which does not fit this pattern.

What concept does this question test?

It tests General physiology: mitochondrial inheritance in Physiology. Mitochondrial disease therefore passes from affected mothers to all offspring and not from affected fathers.

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 General physiology: mitochondrial inheritance?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.