[A]: Haemophillia is a genetically linked dis- ease.
[R]: The carrier gene is present on X chromosome of female

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 Haemophilia**:
- Haemophilia is a genetic disorder that affects the blood's ability to clot. This leads to excessive bleeding even from minor injuries.
- It is classified as an X-linked recessive disorder, meaning the gene responsible for haemophilia is located on the X chromosome.

2. **Types of Haemophilia**:
- There are two main types of haemophilia:
- **Haemophilia A**: Caused by a deficiency of clotting factor VIII.
- **Haemophilia B**: Caused by a deficiency of clotting factor IX.

3. **Genetic Basis**:
- Males have one X and one Y chromosome (XY). If the X chromosome carries the mutated gene for haemophilia, the male will be affected because there is no corresponding gene on the Y chromosome to counteract it.
- Females have two X chromosomes (XX). If a female has one mutated gene on one X chromosome, she becomes a carrier but does not show symptoms of the disease unless both X chromosomes carry the mutated gene.

4. **Assertion and Reason Analysis**:
- **Assertion (A)**: "Haemophilia is a genetically linked disease."
- This statement is true because haemophilia is indeed a genetic disorder linked to specific genes on the X chromosome.
- **Reason (R)**: "The carrier gene is present on the X chromosome of female."
- This statement is also true. The carrier gene for haemophilia is located on the X chromosome in females.

5. **Correct Explanation**:
- While both statements are true, the reason does not correctly explain the assertion. The assertion is about haemophilia being a genetically linked disease, while the reason specifically addresses the carrier status in females. Therefore, the reason does not provide a direct explanation for the assertion.

6. **Conclusion**:
- Since both the assertion and reason are true, but the reason is not the correct explanation for the assertion, the correct option is: "Both assertion and reason are true, but reason is not the correct explanation."

**Final Answer**: Both assertion and reason are true; reason is not the correct explanation.

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