Genes for which of the following can serve as selectable marker ?

Options

A. `beta`-galactosidase
B. Ampicillin
C. Tetracycline
D. All of these

Answer

### Step-by-Step Solution:

1. **Understanding Selectable Markers**: Selectable markers are genes that confer a trait suitable for artificial selection. They help in identifying and selecting the cells that have successfully taken up the foreign DNA (transformants) from those that have not (non-transformants).

2. **Role of Selectable Markers in Recombinant DNA Technology**: In recombinant DNA technology, a foreign gene is inserted into a vector (like a plasmid). When this vector is introduced into a host cell, not all cells will take up the vector with the foreign gene. Selectable markers help in distinguishing the transformed cells from the non-transformed ones.

3. **Examples of Selectable Markers**: Common selectable markers include antibiotic resistance genes (like those for ampicillin and tetracycline) and reporter genes (like the LacZ gene which encodes beta-galactosidase).

4. **Beta-Galactosidase and LacZ Gene**: The LacZ gene is a commonly used selectable marker in molecular cloning. When the foreign DNA is inserted into the LacZ gene, it disrupts the gene and prevents the production of beta-galactosidase.

5. **Colony Color Indication**:
- **White Colonies**: If the LacZ gene is disrupted (due to the insertion of foreign DNA), beta-galactosidase is not produced, and the colonies appear white. This indicates that the cells are transformed (they have taken up the foreign DNA).
- **Blue Colonies**: If the LacZ gene is intact (no foreign DNA inserted), beta-galactosidase is produced, and the colonies appear blue. This indicates that the cells are non-transformed (they have not taken up the foreign DNA).

6. **Conclusion**: The genes that can serve as selectable markers include the LacZ gene (beta-galactosidase), as well as antibiotic resistance genes like those for ampicillin and tetracycline.

### Final Answer:
The genes that can serve as selectable markers include the LacZ gene (beta-galactosidase) and antibiotic resistance genes (like ampicillin and tetracycline).

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