23. Two classes of genes – proto-oncogene and tumor suppressor gene usually contribute to the development of cancer.

Following are some of the statements regarding both the genes.
A. Proto-oncogenes result in the development Of cancer by gain-of-function mutation whereas tumor suppressor gene leads to cancer development by loss-of-function mutation.
B. Proto-oncogenes result in development of cancer by loss-of-function whereas mutation
tumor suppressor gene leads to cancer development by gain of-function mutation.
C. Mutation in both the alleles of a protooncogene is required for induction of cancer whereas mutation in one of the two alleles in tumor suppressor gene is sufficient for promoting tumorigenesis.
D. Mutation in one of the two alleles in proto-oncogene is sufficient for induction of cancer

whereas mutation in both the alleles of a tumor suppressor gene is required for promoting
tumorigenesis.

Which combinations of the above statements are true for both the genes?
(1) A and B                                             (2) A and C
(3) A and D                                             (4) B and C

 

The correct combination of statements regarding proto-oncogenes and tumor suppressor genes is:

(3) A and D

Explanation:

• Statement A: Proto-oncogenes result in the development of cancer by gain-of-function mutations, where a single mutated allele can increase cell division and contribute to cancer. Tumor suppressor genes lead to cancer development by loss-of-function mutations, requiring both alleles to be inactivated for tumorigenesis.

• Statement D: Mutation in one of the two alleles in a proto-oncogene is sufficient for cancer induction, making it dominant. Conversely, mutation in both alleles of a tumor suppressor gene is typically required to promote tumorigenesis, making it a recessive mechanism.

• Incorrect statements:

  • B: Incorrect, because proto-oncogenes cause cancer by gain of function, not loss of function.

  • C: Incorrect, because oncogene activation usually requires mutation in one allele; tumor suppressor gene mutation usually requires both alleles mutated.

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