GATE 2023 BT – Question 39
The event(s) that lead(s) to inactivation of tumor suppressor genes in cancer cells is(are)
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Correct answer: (B) promoter methylation; (C) loss of heterozygosity
Explanation
A **tumour suppressor gene** works as a brake on cell growth, so it is inactivated by events that remove or silence its function (loss of function).
- **A. Gene amplification:** more copies of a gene, which usually activates **oncogenes** (for example HER2 or MYC). ✗
- **B. Promoter methylation:** methylation of CpG islands silences the gene (epigenetic silencing, as with *p16* and *BRCA1*). ✓
- **C. Loss of heterozygosity:** the second, remaining functional allele is lost (deletion or mitotic recombination), as in Knudson's two-hit model of *RB1* and *TP53*. ✓
- **D. Histone acetylation:** opens chromatin and increases transcription, so it does not inactivate. ✗
Answer **B and C**.