In presence of chromogenic substrate recombinant bacteria gives

Options

A. Red coloured colonies
B. Colourless colonies
C. Blue colonies
D. Green colonies

Answer

To answer the question "In presence of chromogenic substrate recombinant bacteria gives," we will follow these steps:

### Step-by-Step Solution:

1. **Understanding Chromogenic Substrates**:
- Chromogenic substrates are compounds that produce a color change when they are metabolized by specific enzymes. In the context of recombinant bacteria, these substrates help identify whether the bacteria contain a specific recombinant DNA.

2. **Role of Beta-Galactosidase**:
- One of the most commonly used chromogenic substrates is related to the enzyme beta-galactosidase. This enzyme can cleave certain substrates, leading to a color change.

3. **Color Outcomes Based on Enzyme Presence**:
- If the recombinant bacteria express beta-galactosidase, they will metabolize the chromogenic substrate and produce a blue color.
- Conversely, if the bacteria do not express beta-galactosidase due to insertional inactivation (where the gene for the enzyme is disrupted), they will not metabolize the substrate and will appear as colorless or white colonies.

4. **Identifying Recombinant vs Non-Recombinant**:
- In this context, the blue colonies indicate non-recombinant bacteria (those that have not taken up the plasmid containing the gene for beta-galactosidase), while the white colonies indicate recombinant bacteria (those that have taken up the plasmid and have an insertion that disrupts the beta-galactosidase gene).

5. **Conclusion**:
- Therefore, in the presence of a chromogenic substrate, recombinant bacteria will produce white colonies, while non-recombinant bacteria will produce blue colonies. The correct answer to the question is that recombinant bacteria give colorless (or white) colonies.

### Final Answer:
In the presence of chromogenic substrate, recombinant bacteria give **colorless (white) colonies**.

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