The gene which synthesises repressor is

Options

A. Operator gene
B. Regulator gene
C. Promoter gene
D. Structural gene

Answer

To solve the question "The gene which synthesizes repressor is," we will analyze the options provided and determine which one correctly identifies the gene responsible for synthesizing repressor proteins.

### Step-by-Step Solution:

1. **Understanding the Options:**
- **Option A: Operator Gene**
- The operator gene is a segment of DNA that serves as a binding site for repressor proteins. It does not synthesize the repressor; rather, it is where the repressor binds to inhibit transcription. Therefore, this option is incorrect.

2. **Analyzing Option B: Regulator Gene**
- The regulator gene is responsible for producing or synthesizing repressor proteins. These proteins can bind to the operator region of DNA and inhibit the transcription of downstream genes. This makes option B a strong candidate for the correct answer.

3. **Examining Option C: Promoter Gene**
- The promoter gene is a region of DNA that initiates transcription of a particular gene. It is not involved in synthesizing repressor proteins. Therefore, option C is incorrect.

4. **Looking at Option D: Structural Gene**
- A structural gene codes for any RNA or protein product that is not a regulatory factor. It does not synthesize repressor proteins. Hence, option D is also incorrect.

5. **Conclusion:**
- After analyzing all the options, we conclude that the gene which synthesizes repressor is the **Regulator Gene** (Option B).

### Final Answer:
The gene which synthesizes repressor is **Option B: Regulator Gene**.