After insertion of DNA segment within the sequence of Z-gene of bacteria, they are grown on chromogenic substrate. After the growth of bacterial colonies, they are identified as
(i) Recombinants if colonies are blue-coloured
(ii) Recombinants if colonies are white coloured
(iii) Non-recombinants if colonies are blue-coloured
(iv) Non - recombinants if colonies are white coloured

Options

A. iii, iv
B. i, iv
C. i, ii
D. ii, iii

Answer

To solve the question regarding the identification of bacterial colonies after the insertion of a DNA segment within the Z-gene, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Function of the Z-Gene**:
The Z-gene in bacteria encodes for the enzyme beta-galactosidase, which is responsible for breaking down lactose into glucose and galactose.

**Hint**: Remember that the Z-gene is crucial for the production of a specific enzyme.

2. **Insertion of DNA Segment**:
When a foreign DNA segment is inserted into the Z-gene, it leads to the inactivation of this gene. This process is known as "insertional inactivation."

**Hint**: Think about how inserting a new piece of DNA can disrupt the normal function of a gene.

3. **Effect on Colony Color**:
The presence of active beta-galactosidase results in blue-colored colonies when grown on a chromogenic substrate. If the Z-gene is inactivated (due to the insertion), the colonies will not produce the enzyme and will appear white.

**Hint**: Consider the relationship between enzyme activity and the resulting color of the colonies.

4. **Identifying Recombinants and Non-Recombinants**:
- **Recombinants**: These are the colonies where the Z-gene has been inactivated (white colonies).
- **Non-Recombinants**: These are the colonies where the Z-gene remains functional (blue colonies).

**Hint**: Focus on the color of the colonies to distinguish between recombinants and non-recombinants.

5. **Conclusion**:
Based on the above understanding:
- Colonies that are **white** are **recombinants** (due to inactivation of the Z-gene).
- Colonies that are **blue** are **non-recombinants** (due to the active Z-gene).

Therefore, the correct identification is:
- (i) Recombinants if colonies are blue-coloured: **False**
- (ii) Recombinants if colonies are white coloured: **True**
- (iii) Non-recombinants if colonies are blue-coloured: **True**
- (iv) Non-recombinants if colonies are white coloured: **False**

The correct options are (ii) and (iii).

### Final Answer:
- (ii) Recombinants if colonies are white coloured.
- (iii) Non-recombinants if colonies are blue-coloured.