Genetics: penetrance and 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 · Genetics: penetrance and expressivity

Sample item

In a family with autosomal dominant retinoblastoma, a man and his son are affected. The man's father had no tumour but carries the same RB1 mutation. Which term describes this?

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

The answer and the reasoning

B. Reduced (incomplete) penetrance

Penetrance is the proportion of individuals carrying a mutation who show any phenotype. A carrier with no features at all, who transmits to the next generation, is an example of reduced penetrance. Variable expressivity refers to different severity among those who are affected.

Option by option

  • A. Anticipation

    Anticipation is earlier or more severe disease in successive generations, usually with repeat expansions.

  • B. Reduced (incomplete) penetrance (correct)

    Correct. A mutation carrier with no phenotype shows incomplete penetrance.

  • C. Genomic imprinting

    Imprinting depends on the parent of origin of the allele and is not shown by this pedigree.

  • D. Variable expressivity

    Expressivity describes the degree of severity in people who do express the trait.

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, Reduced (incomplete) penetrance. Penetrance is the proportion of individuals carrying a mutation who show any phenotype.

Why is "Anticipation" not the answer?

Anticipation is earlier or more severe disease in successive generations, usually with repeat expansions.

Why is "Genomic imprinting" not the answer?

Imprinting depends on the parent of origin of the allele and is not shown by this pedigree.

Why is "Variable expressivity" not the answer?

Expressivity describes the degree of severity in people who do express the trait.

What concept does this question test?

It tests Genetics: penetrance and expressivity in Anatomy. A carrier with no features at all, who transmits to the next generation, is an example of reduced penetrance. Variable expressivity refers to different severity among those who are affected.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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: penetrance and 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.