During insertional 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 enzyme
1) α -glucosidase
2) restriction endonuclease
3) β -galactosidase
4) Taq polymerase

Options

A. 1) `alpha`-glucosidase
B. 2) restriction endonuclease
C. 3) `beta`-galactosidase
D. 4) Taq polymerase

Answer

To solve the question regarding the enzyme responsible for the blue color produced during insertional inactivation, follow these steps:

### Step-by-Step Solution:

1. **Understand Insertional Inactivation**:
- Insertional inactivation is a technique used in molecular biology where a foreign DNA fragment is inserted into a plasmid vector. This insertion can disrupt the function of a gene present in the plasmid.

2. **Identify the Role of the LacZ Gene**:
- The plasmid often contains the LacZ gene, which encodes the enzyme β-galactosidase. This enzyme is crucial for the metabolism of lactose and is used in molecular cloning as a reporter gene.

3. **Chromogenic Substrate Interaction**:
- When the LacZ gene is functional (i.e., when there is no insert in the plasmid), the β-galactosidase enzyme is produced. This enzyme can act on a chromogenic substrate (like X-gal), leading to the production of a blue color in the colonies.

4. **Effect of Insert on LacZ Gene**:
- If a foreign DNA insert is present in the plasmid, it disrupts the LacZ gene, preventing the production of β-galactosidase. Consequently, the colonies will not produce the blue color and will appear colorless.

5. **Evaluate the Options**:
- Now, we can evaluate the given options:
1. **α-glucosidase** - Incorrect, as this enzyme does not relate to the blue color in this context.
2. **Restriction endonuclease** - Incorrect, as this enzyme is involved in cutting DNA, not in producing color.
3. **β-galactosidase** - Correct, as this enzyme produces the blue color when the LacZ gene is active.
4. **Taq polymerase** - Incorrect, as this enzyme is used in PCR and does not produce color.

6. **Conclusion**:
- The correct answer is option **3) β-galactosidase**.