In Lederberg's replica what shall be used to obtain streptomycin resistant strain ?

Options

A. Minimal medium and streptomycin
B. Complete medium and streptomycin
C. Only minimal medium
D. Only complete medium.

Answer

### Step-by-Step Solution:

1. **Understanding the Experiment**: Lederberg's replica plating experiment is designed to demonstrate the genetic basis of adaptation in bacteria. The aim is to identify bacteria that are resistant to the antibiotic streptomycin.

2. **Preparing the Master Plate**: A master plate is prepared with a complete culture medium that contains all the essential nutrients required for bacterial growth. This medium allows for the growth of various bacterial colonies.

3. **Inoculating the Master Plate**: A bacterial suspension is added to the master plate, allowing colonies to grow. Each colony represents a genetically distinct strain of bacteria.

4. **Creating the Replica Plate**: A sterile velvet cloth is pressed onto the master plate to pick up imprints of the colonies. This cloth is then pressed onto a new agar plate, creating a replica plate that contains the same arrangement of colonies.

5. **Adding Antibiotics**: The replica plate is then divided into two conditions:
- Condition 1: Complete medium without any antibiotics.
- Condition 2: Complete medium with streptomycin added.

6. **Observing Colony Growth**: In the presence of streptomycin, some colonies will survive while others will not. The colonies that survive indicate that they have a natural resistance to streptomycin, likely due to pre-existing mutations.

7. **Identifying Resistant Strains**: The surviving colonies on the streptomycin plate are identified as the streptomycin-resistant strains. The colonies that do not survive are sensitive to the antibiotic.

8. **Conclusion**: To obtain a streptomycin-resistant strain, a complete medium with streptomycin must be used. This allows for the selection of bacteria that have developed resistance through mutation.

### Final Answer:
To obtain a streptomycin-resistant strain in Lederberg's replica plating experiment, a **complete medium with streptomycin** must be used.

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