In genetic engineering, the antibiotics are used

Options

A. as sequences from where replication starts
B. to keep the culture free of infection
C. as selectable markers
D. to select healty vectors

Answer

### Step-by-Step Solution:

1. **Understanding Genetic Engineering**: Genetic engineering involves manipulating an organism's DNA to achieve desired traits or produce specific products. This can include cloning genes, modifying organisms, or creating genetically modified organisms (GMOs).

2. **Role of Antibiotics**: In the context of genetic engineering, antibiotics are substances that kill or inhibit the growth of bacteria. They are crucial in laboratory settings to ensure that unwanted bacterial growth does not interfere with the experiment.

3. **Selectable Markers**: Antibiotics are often used as selectable markers in genetic engineering. A selectable marker is a gene that provides a way to select for cells that have been successfully transformed with a plasmid or vector containing the gene of interest.

4. **Application of Selectable Markers**: When a vector containing an antibiotic resistance gene is introduced into a host cell, only those cells that have taken up the vector will survive in the presence of the antibiotic. This allows researchers to easily identify and isolate the cells that have been successfully modified.

5. **Conclusion**: Therefore, in genetic engineering, antibiotics are primarily used as selectable markers to identify and select for cells that have successfully incorporated the desired genetic material.

### Final Answer:
In genetic engineering, antibiotics are used as selectable markers to select for cells that have successfully taken up the genetic material, allowing researchers to identify and isolate healthy vectors.

---