In the technique of selection of transformed , recombinant host cell by insertional inactivation method, the correct statements is .

Options

A. The enzyme `beta` - galactoside is inactivated by the presence of desired alien gene in the medium
B. Cells of blue coloured colonies turn colorles due to insertion fo desired gene in the amino acid sequence of the enzyme `beta` - galactosidase
C. `beta` - galactoside gene is inactivated due to insertion of desired gene in the amino acid sequence of the enzyme `beta` - galactoside
D. Colonies of normal host cell which do not contain an insert do not produce blue colour in the absence of suitable chromogenic substrate in the medium.

Answer

**Step-by-Step Solution:**

1. **Understanding Insertional Inactivation:**
- Insertional inactivation is a method used to identify transformed cells by inserting a desired gene into a gene that produces an enzyme, usually beta-galactosidase. This method serves as an alternative to traditional selectable markers.

2. **Role of Beta-Galactosidase:**
- Beta-galactosidase is an enzyme that can hydrolyze certain substrates to produce a color change. When the gene for beta-galactosidase is intact, the bacteria will produce a blue color when grown on a specific medium containing a chromogenic substrate.

3. **Insertion of Desired Gene:**
- When the desired gene is inserted into the beta-galactosidase gene, it inactivates the enzyme. This means that the bacteria will not be able to produce the enzyme, leading to a colorless colony when grown on the chromogenic substrate.

4. **Color Differentiation:**
- If the bacteria are transformed and contain the recombinant DNA (with the desired gene inserted), they will appear colorless. Conversely, if the bacteria do not have the recombinant DNA (normal host cells), they will produce blue colonies due to the presence of functional beta-galactosidase.

5. **Evaluating the Statements:**
- **Statement 1:** Incorrect. The inactivation occurs due to the insertion of the gene into the beta-galactosidase gene, not just its presence in the medium.
- **Statement 2:** Incorrect. Blue colonies indicate the presence of beta-galactosidase, which means the desired gene was not inserted.
- **Statement 3:** Correct. The insertion of the desired gene into the beta-galactosidase gene inactivates it.
- **Statement 4:** Incorrect. Normal host cells produce blue colonies due to the presence of the functional beta-galactosidase enzyme.

6. **Conclusion:**
- The correct statement regarding the insertional inactivation method is that the beta-galactosidase chain is inactivated due to the insertion of the desired gene.

**Final Answer:**
- The correct statement is: "Beta-galactosidase chain is inactivated due to insertion of desired gene."

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