Molecular biology and genetics: haploinsufficiency: practice question

A Biochemistry 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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Biochemistry · Molecular biology and genetics: haploinsufficiency

Sample item

In an autosomal dominant disorder, a heterozygous whole-gene deletion leaves a single working allele that produces only 50 percent of the normal protein, which is insufficient for normal function. What is this mechanism called?

AHaploinsufficiencyBDominant-negative effectCGain of functionDGenomic imprinting

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

The answer and the reasoning

A. Haploinsufficiency

In haploinsufficiency one functional copy cannot produce enough gene product for normal function. A dominant-negative mutant protein instead interferes with the normal protein, and gain of function creates a new activity. Familial hypercholesterolaemia due to LDL receptor loss is an example.

Option by option

A. Haploinsufficiency (correct)
Correct. Half the normal dose is not enough, so the heterozygote is affected.
B. Dominant-negative effect
A dominant-negative effect needs an abnormal protein that disrupts the normal one, but here the allele is deleted.
C. Gain of function
Gain of function means an abnormal or increased activity, not a lower dose.
D. Genomic imprinting
Imprinting depends on the parent of origin and not on the dose from deletion.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is A, Haploinsufficiency. In haploinsufficiency one functional copy cannot produce enough gene product for normal function.

Why is "Dominant-negative effect" not the answer?

A dominant-negative effect needs an abnormal protein that disrupts the normal one, but here the allele is deleted.

Why is "Gain of function" not the answer?

Gain of function means an abnormal or increased activity, not a lower dose.

Why is "Genomic imprinting" not the answer?

Imprinting depends on the parent of origin and not on the dose from deletion.

What concept does this question test?

It tests Molecular biology and genetics: haploinsufficiency in Biochemistry. A dominant-negative mutant protein instead interferes with the normal protein, and gain of function creates a new activity. Familial hypercholesterolaemia due to LDL receptor loss is an example.

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 Molecular biology and genetics: haploinsufficiency?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.