Medical genetics: variable expressivity: 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: variable expressivity

Sample item

A mother with neurofibromatosis type 1 has only a few cafe-au-lait spots and axillary freckling. Her son, with the same mutation, has numerous neurofibromas and an optic glioma. What is this difference in severity called?

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

The answer and the reasoning

D. Variable expressivity

Variable expressivity means that people with the same genotype show different degrees of the phenotype. Neurofibromatosis type 1 shows very wide variation in severity even within one family.

Option by option

  • A. Anticipation

    Anticipation refers to progressive worsening across generations through repeat expansion, which does not occur in this disorder.

  • B. Mosaicism

    Mosaicism means different cell lines in one person and does not explain a difference between relatives.

  • C. Reduced penetrance

    Reduced penetrance means a mutation carrier shows no phenotype at all, but both of these individuals are affected.

  • D. Variable expressivity (correct)

    Correct. The same mutation produces a mild phenotype in one person and a severe one in another.

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 D, Variable expressivity. Variable expressivity means that people with the same genotype show different degrees of the phenotype.

Why is "Anticipation" not the answer?

Anticipation refers to progressive worsening across generations through repeat expansion, which does not occur in this disorder.

Why is "Mosaicism" not the answer?

Mosaicism means different cell lines in one person and does not explain a difference between relatives.

Why is "Reduced penetrance" not the answer?

Reduced penetrance means a mutation carrier shows no phenotype at all, but both of these individuals are affected.

What concept does this question test?

It tests Medical genetics: variable expressivity in Anatomy. Neurofibromatosis type 1 shows very wide variation in severity even within one family.

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: variable expressivity?

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.