The antibiotics are used as _______ in genetic engineering.

Correct option is A

Antibiotics are used as selectable markers in genetic engineering. They help identify cells that have successfully incorporated a recombinant plasmid by allowing growth in the presence of the antibiotic.
Definition:
· A selectable marker is a gene introduced into a host organism that allows for the identification and selection of successfully transformed cells or organisms.
Purpose:
· Selectable markers help distinguish cells that have taken up the desired genetic material from those that have not.
Types of Selectable Markers:
· Antibiotic Resistance Markers:
· Provide resistance to specific antibiotics.
· Example: ampR (ampicillin resistance), kanR (kanamycin resistance).
· Herbicide Resistance Markers:
· Commonly used in plant genetic engineering.
· Example: bar gene (resistance to phosphinothricin), cp4 epsps (resistance to glyphosate).
· Metabolic Markers:
· Enable the host to grow in selective media by providing essential enzymes.
· Example: lacZ (encodes β-galactosidase), his3 (histidine biosynthesis in yeast).
Mechanism of Action:
· After transformation, the host cells are exposed to a selective agent (e.g., antibiotic, herbicide).
· Only those cells with the selectable marker gene survive and grow, confirming successful transformation.
Examples in Genetic Engineering:
· pBR322 Plasmid:
· Contains two selectable markers: ampR and tetR, conferring resistance to ampicillin and tetracycline, respectively.
· Agrobacterium tumefaciens Ti Plasmid:
· Often modified with selectable markers for plant transformation.
Application:
· Genetic Engineering:
· Ensures the introduction and maintenance of foreign DNA in host cells.
· Plant and Animal Biotechnology:
· Used to develop genetically modified organisms (GMOs) resistant to diseases, pests, or environmental stressors.
· Molecular Biology Research:
· Simplifies the screening of transformed cells in cloning experiments.
Common Selective Agents:
· Antibiotics: Ampicillin, Kanamycin, Chloramphenicol.
· Herbicides: Glyphosate, Phosphinothricin.