A plasmid has two antibiotic-resistance genes, one for tetracycline and other for ampicillin. It is treated with a restriction enzyme that cuts in the middle of the ampicillin gene. DNA fragments containing a haemoglobin gene were cut with the same enzyme. The plasmids and fragments are mixed, treated with ligase and used to transform bacterial cells. Clones that have taken up the recombinant DNA are the ones that

Options

A. can grow on plates with both antibiotics
B. can grow on plates with ampicillin but not with tetracycline
C. can grow on plates with tetracycline but not with ampicillin
D. cannot grow with any antibiotic

Answer

To solve the question, we need to analyze the process of creating recombinant DNA using a plasmid that has been modified and understand the implications of the antibiotic resistance genes involved.

### Step-by-Step Solution:

1. **Understanding the Plasmid Structure**: The plasmid contains two antibiotic-resistance genes: one for tetracycline and one for ampicillin.

2. **Restriction Enzyme Action**: The plasmid is treated with a restriction enzyme that cuts the DNA in the middle of the ampicillin resistance gene. This means that the ampicillin gene is disrupted and will not function properly.

3. **Preparation of Hemoglobin Gene**: DNA fragments containing a hemoglobin gene are also cut with the same restriction enzyme. This ensures that the ends of the hemoglobin gene fragment are compatible with the cut site in the plasmid.

4. **Ligation Process**: The cut plasmid and the hemoglobin gene fragments are mixed together and treated with ligase. The ligase enzyme facilitates the joining of the hemoglobin gene into the plasmid at the site where the ampicillin gene was cut.

5. **Transformation into Bacterial Cells**: The recombinant plasmids (now containing the hemoglobin gene instead of the ampicillin resistance gene) are introduced into bacterial cells through a process called transformation.

6. **Selection of Clones**: After transformation, the bacteria are plated on media containing antibiotics. The key point here is to determine which bacteria have successfully taken up the recombinant plasmid:
- **Bacteria with recombinant DNA**: These bacteria will have the tetracycline resistance gene from the original plasmid but will lack the functional ampicillin resistance gene since it was disrupted by the insertion of the hemoglobin gene.

7. **Testing Growth on Antibiotic Plates**:
- **On plates with both antibiotics**: The bacteria will not grow because they cannot resist ampicillin.
- **On plates with ampicillin only**: The bacteria will not grow since they lack the ampicillin resistance gene.
- **On plates with tetracycline only**: The bacteria will grow because they still possess the tetracycline resistance gene.
- **On plates with no antibiotics**: The bacteria will grow as there is no selection pressure.

### Conclusion:
The clones that have taken up the recombinant DNA are the ones that can grow on plates with tetracycline but not with ampicillin.