A: Selection of recombinants due to inactivation of antibiotics is cumbersome procedure.
R: It requires simultaneous plating on two plates having different antibiotics.

Options

A. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion then mark (2).
C. If Assertion is true but Reason are false, then mark(3).
D. If both Assertion and Reason are false, then mark(4).

Answer

To solve the assertion-reason question, we need to analyze both the assertion (A) and the reason (R) provided in the question.

### Step 1: Understand the Assertion (A)
The assertion states that "Selection of recombinants due to inactivation of antibiotics is a cumbersome procedure." This means that the process of identifying which bacteria have successfully taken up recombinant DNA (which may confer antibiotic resistance) is not straightforward and involves complexity.

### Step 2: Understand the Reason (R)
The reason states that "It requires simultaneous plating on two plates having different antibiotics." This indicates that in order to distinguish between recombinant and non-recombinant bacteria, two different types of antibiotic media must be used to grow the bacteria.

### Step 3: Analyze the Process
1. **Example of Antibiotic Resistance**: Consider a plasmid (like pBR322) that has genes for resistance to two antibiotics: tetracycline and ampicillin.
2. **Insertion of Foreign DNA**: If foreign DNA is inserted into the tetracycline resistance gene, the bacteria that take up this plasmid will lose the ability to resist tetracycline but will still be able to resist ampicillin.
3. **Simultaneous Plating**: To identify which bacteria are recombinants (those that have taken up the foreign DNA), you need to plate the bacteria on two different media:
- One plate with tetracycline (where recombinants will not grow).
- One plate with ampicillin (where both recombinants and non-recombinants will grow).
4. **Selection of Recombinants**: After incubation:
- Non-recombinants will grow on both plates.
- Recombinants will only grow on the ampicillin plate and not on the tetracycline plate.

### Step 4: Conclusion
Since the process requires the use of two different antibiotic plates to distinguish between recombinant and non-recombinant bacteria, it is indeed cumbersome. Therefore, both the assertion and the reason are true, and the reason correctly explains the assertion.

### Final Answer
Both assertion (A) and reason (R) are true, and R correctly explains A.

---