Some genes are constantly expressed in the bacterial cells. These genes are called:

Options

A. Luxury genes
B. Constitutive genes
C. Non-constitutive genes
D. More than one option is correct.

Answer

To answer the question about which genes are constantly expressed in bacterial cells, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Gene Expression**:
- Genes can be expressed at different levels depending on the needs of the cell. Some genes are always "on," while others are only activated under specific conditions.

2. **Identifying Types of Genes**:
- **Luxury Genes**: These genes are specific to certain tissues or organs and are not expressed in all cells. They are only activated when their function is needed.
- **Constitutive Genes**: These genes are continuously expressed and are essential for basic cellular functions. They are required in all cell types and are always "on."
- **Non-Constitutive Genes**: These are similar to luxury genes and are not always expressed. They can be turned on or off based on cellular needs.

3. **Analyzing the Options**:
- The question provides four options: luxury genes, constitutive genes, non-constitutive genes, and more than one option is correct.
- Since luxury genes and non-constitutive genes are not expressed constantly, they do not fit the criteria for the question.

4. **Conclusion**:
- The only type of gene that is constantly expressed in bacterial cells is the **constitutive gene**. These genes are essential for maintaining basic cellular functions and are always active.

### Final Answer:
The genes that are constantly expressed in bacterial cells are called **constitutive genes**.

---