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GATE 2020 BT Q.10: solution and answer

GATE 2020 · BTQ.10 · 1 mark · MCQ

A vector derived from which one of the following viruses is used for high-frequency genomic integration of a transgene in animal cells?

  1. (A)

    Adenovirus

  2. (B)

    Adeno-associated virus

  3. (C)

    Lentivirus

  4. (D)

    Herpes simplex virus

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Answer and solution

ANSWER

The correct answer is (C) Lentivirus.

Official answer: CSource: Official answer key, GATE 2020 BT (IIT Delhi)

  1. Requirement: "high-frequency genomic integration" means the transgene must be efficiently and stably inserted into host chromosomal DNA, not merely delivered as an episome.

  2. (A) Adenovirus: adenoviral vectors remain episomal in the nucleus and give only transient expression — eliminate.

  3. (B) Adeno-associated virus (AAV): recombinant AAV vectors persist mainly as episomal concatemers; true chromosomal integration is rare and random (only wild-type AAV integrates efficiently and site-specifically at AAVS1, and that is not the vector form used) — eliminate.

  4. (C) Lentivirus: lentiviral (retroviral) vectors encode an integrase that inserts the reverse-transcribed proviral DNA into the host genome as part of their normal life cycle, giving efficient, stable, high-frequency integration — and they do this even in non-dividing cells, which is why they are the standard choice for stable transgene integration in animal cells.

  5. (D) Herpes simplex virus (HSV): HSV-based vectors are maintained episomally in the nucleus (useful for large payloads and neuronal delivery) and do not integrate at high frequency — eliminate.

  6. By elimination and by the defining integrase-driven mechanism of lentiviral vectors, the correct answer is (C) Lentivirus.

KEY IDEA

Stable, high-frequency integration of a transgene into the host chromosome requires a viral vector encoding an integrase enzyme; among common animal-cell gene delivery vectors, only lentiviral (retroviral) vectors carry this and can integrate even into non-dividing cells.

WATCH OUT FOR

Confusing AAV's ability to persist long-term in cells (as episomal concatemers, or via rare/random integration) with true high-frequency, integrase-driven integration — AAV is favoured precisely because it is largely non-integrating and safer, the opposite property being tested here.

From the GATE 2020 BT paper. Every question of this paper · Download the full paper · All 10 Enzymes & vectors questions, with notes

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