How are transformants selected from nontransformants

Options

A. Presence of more than one recognition site in vector DNA
B. Presence of alein DNA into vector DNA results into insertional inactivation of selectable marker
C. Antibiotic resistance gene gets inactivated due to insertion of alein DNA
D. Both B and C

Answer

To answer the question "How are transformants selected from non-transformants?", we can break down the process into several key steps:

### Step-by-Step Solution:

1. **Understanding Transformants and Non-Transformants**:
- Transformants are cells that have successfully taken up foreign DNA (recombinant DNA) via a vector.
- Non-transformants are those that have not taken up the foreign DNA.

2. **Using a Cloning Vector**:
- A common vector used in molecular biology is the pBR322 plasmid, which contains genes that confer resistance to antibiotics, such as ampicillin and tetracycline. These genes act as selectable markers.

3. **Insertion of Foreign DNA**:
- When foreign DNA is inserted into the vector, it often disrupts one of the antibiotic resistance genes (e.g., the ampicillin resistance gene). This process is known as insertional inactivation.

4. **Culturing on Selective Media**:
- The transformed bacteria (transformants) are cultured on agar plates that are coated with antibiotics (e.g., ampicillin).
- Transformants that have taken up the foreign DNA will not be able to grow on the ampicillin-coated plates because they have lost the ability to resist the antibiotic due to the disruption of the ampicillin resistance gene.

5. **Observation of Growth**:
- Non-transformants, which still possess the ampicillin resistance gene, will grow and form colonies on the ampicillin-coated plates.
- Thus, after incubation, the plates will show no growth of transformants (which are sensitive to ampicillin) while non-transformants will form visible colonies.

6. **Alternative Methods**:
- Another method for selecting transformants is the color-coded method, where the presence of foreign DNA leads to colorless colonies (due to insertional inactivation of a color-producing gene), while non-transformants produce blue colonies (indicating they have not taken up the foreign DNA).

7. **Conclusion**:
- By using selective media and observing the growth patterns or color changes, researchers can effectively distinguish between transformants and non-transformants.