Carcinogenesis and Oncogenes MCQ — NEET PG Practice Question | NEETPGAI
Carcinogenesis and Oncogenes
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microscope Pathology
All of the following are characteristics of oncogenes EXCEPT:
A. They act in a recessive manner, requiring both alleles to be mutated for phenotypic expression
B. They can be activated by point mutations, gene amplification, or chromosomal translocation
C. They encode proteins that promote cell growth and proliferation
D. They are derived from normal cellular genes called proto-oncogenes
Explanation
Oncogenes: Definition and Mechanism
Key Point
Oncogenes are mutated or overexpressed versions of normal proto-oncogenes that drive cellular transformation. They act in a DOMINANT manner — only one mutated copy is needed to confer a growth advantage.
Dominant vs. Recessive Inheritance Pattern
Oncogenes exhibit dominant inheritance at the cellular level:
A single mutated allele is sufficient to promote transformation
The mutant protein product actively drives proliferation or blocks apoptosis
This contrasts with tumor suppressors (e.g., p53, Rb), which are recessive — both copies must be lost
Mechanisms of Oncogene Activation
Table
Mechanism
Example
Outcome
Point mutation
RAS (codon 12, 13, 61)
Constitutive GTPase activity
Gene amplification
MYC, HER2
Excessive protein production
Chromosomal translocation
BCR-ABL (Philadelphia chromosome)
Abnormal fusion protein
Insertional mutagenesis
Retroviral insertion
Promoter activation
High-YieldNEET PG
The defining feature of oncogenes is their dominant action — one "hit" is enough. This is why a single BCR-ABL fusion in chronic myeloid leukemia drives disease.
Proto-oncogenes
Proto-oncogenes are normal cellular genes encoding:
Growth factors (PDGF)
Growth factor receptors (EGFR, HER2)
Signal transducers (RAS, RAF)
Transcription factors (MYC, JUN)
When mutated or dysregulated, they become oncogenes.
Clinical Pearl
In familial cancer syndromes with germline oncogene mutations (rare), affected individuals inherit one mutated copy and require only a single somatic hit in target tissues — this explains the dominant inheritance pattern seen in families.
Robbins 10e Ch 7
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