During insetional inactivation, the presence of a chromogenic substrate gives blue coloured colonies if the plasmid in the bacteria does not have an insert. The blue colour is produced by the emzyme

Options

A. `alpha`-glucosidase
B. restriction endonuclease
C. `beta`-galactosidase
D. Taq polymerase

Answer

**Step-by-Step Solution:**

1. **Understanding Insertional Inactivation**: Insertional inactivation is a technique used in molecular cloning where a DNA fragment is inserted into a plasmid vector. If the insertion is successful, it disrupts the function of a gene in the plasmid.

2. **Role of Chromogenic Substrate**: In this process, a chromogenic substrate is used to visually distinguish between colonies that have taken up the plasmid with an insert and those that have not.

3. **Color Indication**: When the plasmid does not have an insert, the enzyme associated with the chromogenic substrate remains active, leading to the production of a blue color in the colonies.

4. **Identifying the Enzyme**: The question asks for the specific enzyme responsible for this blue color. We need to evaluate the provided options:
- **Option A: Alpha-glucosidase**: This enzyme breaks down starch but does not produce blue color. Hence, it is incorrect.
- **Option B: Restriction Endonuclease**: This enzyme cuts DNA but does not produce blue color. Hence, it is incorrect.
- **Option C: Beta-galactosidase**: This enzyme acts on the chromogenic substrate to produce a blue color when active. This is the correct answer.
- **Option D: TAG Polymerase**: This enzyme is used in PCR and does not produce blue color. Hence, it is incorrect.

5. **Conclusion**: The correct answer is **Beta-galactosidase**, as it is the enzyme that produces the blue color when the plasmid does not have an insert.

**Final Answer**: Beta-galactosidase

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