Assertion (A) : Haemophilia is an autosomal disorder.
Reason ( R): A haemophilic father can never pass the gene for haemophilia to his son.

Options

A. Both assertion (A) and reason ( R) are true and reason ( R) is the correct explanation of assertion (A).
B. Both assertion (A) and reason ( R) are true but reason ( R) is not the correct explanation of assertion (A).
C. Assertion (A) is true but reason ( R) is false.
D. Assertion (A) is false but reason ( R) is true.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Assertion (A)**: The assertion states that "Haemophilia is an autosomal disorder." To evaluate this, we need to know what an autosomal disorder is. Autosomal disorders are caused by mutations in genes located on autosomes (non-sex chromosomes).

2. **Understanding the Nature of Haemophilia**: Haemophilia is actually classified as a sex-linked recessive disorder, specifically linked to the X chromosome. This means that the gene responsible for haemophilia is located on the X chromosome, not on an autosome.

3. **Evaluating the Reason (R)**: The reason states that "A haemophilic father can never pass the gene for haemophilia to his son." To analyze this, we need to consider the genetic inheritance patterns. A father has one X and one Y chromosome (XY), while a mother has two X chromosomes (XX).

4. **Genetic Transmission**: When a haemophilic father (with the affected X chromosome) has children, he can only pass his Y chromosome to his sons (since sons inherit the Y chromosome from their father). Therefore, the son will inherit the X chromosome from the mother, and not the affected X chromosome from the father.

5. **Conclusion**: Since the assertion is incorrect (haemophilia is not an autosomal disorder) and the reason is correct (a haemophilic father cannot pass the gene to his son), we can conclude that the correct option is: "The assertion is false but the reason is true."

**Final Answer**: The correct option is D: The assertion is false but the reason is true.

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