Which of the following causes mutation (not polyploidy):-

Options

A. Crossing-over
B. NaCl
C. Colchicine
D. `gamma`-rays

Answer

To solve the question "Which of the following causes mutation (not polyploidy)?", we need to analyze the options provided and understand the concepts of mutation and polyploidy.

### Step-by-Step Solution:

1. **Understanding Mutation**:
- Mutation refers to any change in the DNA sequence, which can be caused by various factors. This includes changes in codons, deletions, or inversions that can affect the genetic information.

2. **Understanding Polyploidy**:
- Polyploidy is a condition where an organism has more than two complete sets of chromosomes. This often occurs due to errors in cell division, particularly during meiosis.

3. **Analyzing the Options**:
- **Option A: Crossing Over**:
- Crossing over is a normal process that occurs during meiosis where homologous chromosomes exchange genetic material. It does not cause mutations but rather increases genetic diversity. Therefore, this option does not cause mutation.
- **Option B: NaCl (Sodium Chloride)**:
- NaCl is a common salt present in cells and does not cause mutations. It is essential for various cellular functions but does not alter DNA. Thus, this option does not cause mutation.
- **Option C: Colchicine**:
- Colchicine is a chemical that disrupts spindle fiber formation during cell division, leading to polyploidy by preventing proper chromosome separation. It does not directly cause mutations in the DNA sequence. Therefore, this option does not cause mutation.
- **Option D: Gamma Rays**:
- Gamma rays are a form of ionizing radiation with high energy that can damage DNA. They can cause mutations by breaking DNA strands, leading to deletions or inversions. This option is known to cause mutations.

4. **Conclusion**:
- After analyzing all the options, the correct answer to the question "Which of the following causes mutation (not polyploidy)?" is **Option D: Gamma Rays**.

### Final Answer:
**D. Gamma Rays**