Anatomy and physiology of the eye: inheritance of red-green colour defect: practice question

A Ophthalmology 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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Ophthalmology · Anatomy and physiology of the eye: inheritance of red-green colour defect

Sample item

A boy fails the red-green Ishihara plates. His parents have normal colour vision, but his maternal grandfather has the same defect. What is the most likely mode of inheritance?

AMitochondrialBAutosomal dominantCAutosomal recessiveDX-linked recessive

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

The answer and the reasoning

D. X-linked recessive

The genes for the red and green cone pigments lie on the X chromosome. Colour defects therefore skip through carrier mothers and affect males, with transmission from an affected maternal grandfather to a grandson.

Option by option

A. Mitochondrial
Mitochondrial inheritance passes only through the mother to all children, which does not fit.
B. Autosomal dominant
Autosomal dominant inheritance would show the defect in a parent in each generation.
C. Autosomal recessive
Autosomal recessive inheritance would affect both sexes equally and is not typical here.
D. X-linked recessive (correct)
Correct. The opsin genes are X-linked, so affected males inherit through carrier mothers.

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.

Questions about this Ophthalmology question

What is the answer to this Ophthalmology question?

The best answer is D, X-linked recessive. The genes for the red and green cone pigments lie on the X chromosome.

Why is "Mitochondrial" not the answer?

Mitochondrial inheritance passes only through the mother to all children, which does not fit.

Why is "Autosomal dominant" not the answer?

Autosomal dominant inheritance would show the defect in a parent in each generation.

Why is "Autosomal recessive" not the answer?

Autosomal recessive inheritance would affect both sexes equally and is not typical here.

What concept does this question test?

It tests Anatomy and physiology of the eye: inheritance of red-green colour defect in Ophthalmology. Colour defects therefore skip through carrier mothers and affect males, with transmission from an affected maternal grandfather to a grandson.

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 Anatomy and physiology of the eye: inheritance of red-green colour defect?

Group the red eye by what to examine and what the pupil does. Then use the flashcards and the other Ophthalmology 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.