If a recombinant DNA bearing gene for resistance to antibiotic ampicillin is transferred to E.coli cells, the host cells become transformed into ampicillin resistant cells. If such bacteria are transferred on agar plates containing ampicillin, only transformants will grown and the untransformed recipient cells will die. The ampicillin resistant gene in this case is called as
1) selectable marker
2) recombinant protein
3) cloning site
4) chemical scalpels

Options

A. 1) selectable marker
B. 2) recombinant protein
C. 3) cloning site
D. 4) chemical scalpels

Explanation

To solve the question, we need to analyze the situation described and identify the correct term for the ampicillin resistant gene in the context of recombinant DNA technology. Here’s the step-by-step solution:

### Step-by-Step Solution:

1. **Understanding the Context**: The question describes a scenario where a recombinant DNA (rDNA) containing a gene for ampicillin resistance is introduced into E. coli cells. This process transforms the E. coli cells into ampicillin-resistant cells.

2. **Transformation of E. coli**: When the rDNA is successfully taken up by the E. coli, these cells become resistant to ampicillin. This means they can survive and grow in an environment that contains the antibiotic ampicillin.

3. **Growth on Agar Plates**: The transformed E. coli cells (those that have acquired the rDNA) are then placed on agar plates that contain ampicillin. Only the cells that have been transformed (the transformants) will be able to grow on this medium, while the untransformed cells (those that did not take up the rDNA) will die because they lack the resistance gene.

4. **Identifying the Term**: The question asks for the term that describes the ampicillin resistant gene in this context. Since this gene allows for the selection of transformed cells (those that can survive in the presence of ampicillin), it serves as a means to distinguish between the transformed and untransformed cells.

5. **Conclusion**: The ampicillin resistant gene is referred to as a "selectable marker." Selectable markers are genes that provide a way to identify and select for cells that have taken up the recombinant DNA, as they allow those cells to survive in selective conditions (in this case, the presence of ampicillin).

### Final Answer:
The ampicillin resistant gene in this case is called a **selectable marker** (Option 1).

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