[A]: Lampbrush chromosomes are found in the oocytes of certain animals during the prophase of meiosis. Such chromosomes consist of two central strands along which fine loops extend laterally.
[R]: The loops are thought to be active regions of RNA synthesis

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

### Step-by-Step Solution:

1. **Understanding Lampbrush Chromosomes**:
- Lampbrush chromosomes are specialized structures found in the oocytes of certain animals during the prophase of meiosis, specifically during the diplotene stage of prophase I. They were first discovered by the scientist Jacques Loeb in 1892.

2. **Structure of Lampbrush Chromosomes**:
- These chromosomes consist of two central strands (chromatids) that are connected, with fine loops extending laterally from these central strands. The loops are formed due to the stretching of the chromosome during this stage.

3. **Function of Lampbrush Chromosomes**:
- The loops of the lampbrush chromosomes are believed to be active regions for RNA synthesis. This means that they play a crucial role in the production of RNA, which is essential for protein synthesis and other cellular functions.

4. **Evaluating the Assertion and Reason**:
- The assertion states that lampbrush chromosomes are found in the oocytes of certain animals during meiosis, which is true.
- The reason states that the loops are thought to be active regions of RNA synthesis, which is also true.

5. **Determining the Relationship**:
- Since both the assertion and the reason are true, and the reason provides a correct explanation for the assertion (the loops are indeed involved in RNA synthesis, which is significant for the function of lampbrush chromosomes), we conclude that the correct option is that both assertion and reason are true, and the reason is the correct explanation of the assertion.

### Conclusion:
- The correct answer is: **Option 1: Both assertion and reason are true, and reason is the correct explanation of assertion.**