Assertion: A chromosomes with equal sized arms is called isobrachial.
Reason: Barr bodies are present in the cells of human females.

Options

A. If both As and R are correct and R is correct explanation of As
B. If both As and R are correct but R is not correct explanation of As
C. If As is correct, R is wrong
D. If both As and R are wrong.

Answer

To solve the assertion and reason question, we will break it down into steps:

### Step 1: Analyze the Assertion
The assertion states: "A chromosome with equal sized arms is called isobrachial."

- **Understanding Chromosome Structure**: Chromosomes consist of two arms (P and Q) divided by a centromere.
- **Definition of Isobrachial**: A chromosome with equal-sized arms is indeed referred to as isobrachial, but it is more commonly known as a metacentric chromosome.

### Conclusion for Step 1
The assertion is true because isobrachial chromosomes have equal-sized arms.

### Step 2: Analyze the Reason
The reason states: "Barr bodies are present in the cells of human females."

- **Understanding Barr Bodies**: Barr bodies are the inactivated X chromosomes found in females. Since females have two X chromosomes, one is randomly inactivated and forms a Barr body.
- **Relevance of the Reason**: This statement is true, but it does not explain the assertion about isobrachial chromosomes.

### Conclusion for Step 2
The reason is true, but it does not provide a correct explanation for the assertion.

### Final Conclusion
Both the assertion and reason are true, but the reason is not the correct explanation of the assertion. Therefore, the correct answer is that both the assertion and reason are correct, but the reason does not explain the assertion.