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GENETICS, CELL AND MOLECULAR BIOLOGY · POPULATION & EVOLUTION

GATE 2020 BT, question 3: Population & evolution — solution and answer

GATE 2020 · BTQ.3 · 1 mark · MCQ Checked against the official key

Which of the following statements are CORRECT?

[P] Viruses can play a role in causing human cancer

[Q] A tumor suppressor gene can be turned off without any change in its DNA sequence

[R] Alteration in miRNA expression levels contributes to the development of cancer

  1. (A)

    P and Q only

  2. (B)

    Q and R only

  3. (C)

    P and R only

  4. (D)

    P, Q and R

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Answer and worked solution

ANSWER

All three statements — P, Q and R — are correct, so option (D) is the answer.

Official key: D · Official answer key printed with the GATE 2020 BT paper (IIT Delhi)

  1. Statement P: Certain viruses are well-established causes of human cancer — high-risk HPV's E6/E7 oncoproteins degrade p53 and Rb; Hepatitis B/C virus infection is linked to liver cancer; EBV is linked to lymphomas and nasopharyngeal carcinoma. P is TRUE.

  2. Statement Q: A tumor suppressor gene can be functionally silenced by epigenetic mechanisms — promoter CpG-island hypermethylation or histone deacetylation — which switch off transcription without changing the DNA sequence itself. Q is TRUE.

  3. Statement R: microRNAs post-transcriptionally regulate oncogenes and tumor suppressor genes; overexpression of an oncogenic miRNA or loss of a tumor-suppressive miRNA disrupts this regulatory balance and contributes to tumorigenesis. R is TRUE.

  4. Since P, Q and R are all correct, the matching option is (D) P, Q and R.

KEY IDEA

Cancer can arise from genetic changes (mutations, viral oncogene insertion) and from epigenetic/regulatory changes (promoter hypermethylation silencing tumor suppressors, dysregulated miRNA networks) — DNA sequence alteration is not the only route to malignant transformation.

COMMON MISTAKE

Assuming a tumor suppressor gene can only be inactivated by a mutation in its DNA sequence, and overlooking that epigenetic silencing (e.g., CpG-island hypermethylation of its promoter) achieves the same functional loss without altering the sequence — this leads students to wrongly mark Q as false and pick option (C) instead of (D).

From the GATE 2020 BT paper. Every question of this paper · Download the full paper · All 11 Population & evolution questions, with notes

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