Question

Which of the following mutations is most likely to contribute to the development of cancer?

• A. Loss-of-function mutation in a tumor suppressor gene.
• B. Gain-of function in a DNA repair enzyme.
• C. Silent mutation in a proto-oncogene.
• D. Deletion of non-coding intronic regions in a tumor suppressor gene.

Hint:

Remember the car analogy for cancer genetics:

\textbf{Proto-oncogenes} are the accelerator. Cancer mutation is a \textbf{gain-of-function} (accelerator stuck down).
\textbf{Tumor suppressor genes} are the brakes. Cancer mutation is a \textbf{loss-of-function} (brakes fail).

Answer 1

The Correct Option is A

Step 1: Concept Overview:
Cancer arises from uncontrolled cell growth, often due to gene mutations affecting the cell cycle. Proto-oncogenes and tumor suppressor genes are key players.
Step 2: Detailed Analysis:
Assessing each mutation's impact on cancer risk:

(A) Tumor Suppressor Gene Loss-of-Function: Tumor suppressor genes (e.g., p53, Rb) normally inhibit cell division, acting like "brakes." A loss-of-function mutation disables these "brakes," allowing mutated cells to proliferate and potentially cause cancer. This is a frequent cancer development mechanism.

(B) DNA Repair Enzyme Gain-of-Function: DNA repair enzymes correct mutations. Increased function would enhance mutation repair, {decreasing} cancer risk.

(C) Proto-oncogene Silent Mutation: Proto-oncogenes promote cell division. They require a gain-of-function mutation to become oncogenes. A silent mutation doesn't alter the protein sequence or function, so it won't promote cancer.

(D) Tumor Suppressor Gene Intron Deletion: Introns are removed from mRNA before protein synthesis. Intron deletion is unlikely to affect the final protein unless it disrupts splice sites or regulatory sequences. This is less likely to cause loss of function than a coding region mutation.

Step 3: Conclusion:
A loss-of-function mutation in a tumor suppressor gene is the most likely option to contribute to cancer, as it impairs a critical cell division control.