Special senses: colour vision: 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 · Special senses: colour vision

Sample item

A man with red-green colour blindness marries a woman with normal vision whose family has no colour blindness. What are the expected outcomes in their children?

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

The answer and the reasoning

D. All daughters are carriers and no sons are affected

Red and green cone pigment genes lie on the X chromosome, so the defects are X-linked recessive. The father gives his only X to all daughters, making them carriers, and his Y to sons, who receive the mother's normal X and are unaffected.

Option by option

  • A. Half the daughters are affected

    Daughters have a normal maternal X and are heterozygous, not affected.

  • B. Half the sons are affected and all daughters are normal

    Sons receive the mother's normal X, so they are not affected.

  • C. All sons are affected and all daughters are normal

    Sons inherit the Y from the father and are not affected, and daughters are carriers.

  • D. All daughters are carriers and no sons are affected (correct)

    Correct. Daughters receive the father's affected X and sons do not.

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 D, All daughters are carriers and no sons are affected. Red and green cone pigment genes lie on the X chromosome, so the defects are X-linked recessive.

Why is "Half the daughters are affected" not the answer?

Daughters have a normal maternal X and are heterozygous, not affected.

Why is "Half the sons are affected and all daughters are normal" not the answer?

Sons receive the mother's normal X, so they are not affected.

Why is "All sons are affected and all daughters are normal" not the answer?

Sons inherit the Y from the father and are not affected, and daughters are carriers.

What concept does this question test?

It tests Special senses: colour vision in Physiology. The father gives his only X to all daughters, making them carriers, and his Y to sons, who receive the mother's normal X and are unaffected.

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 Special senses: colour vision?

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.