Haemophilia is transmitted from normal carrier female to male progeny because it is

Options

A. X-linked dominant trait
B. X-linked recessive trait
C. A recessive autosomal trait
D. Y-linked dominant trait

Answer

**Step-by-Step Solution:**

1. **Understanding Haemophilia**: Haemophilia is a genetic disorder that affects the blood's ability to clot. This condition is primarily caused by a deficiency in clotting factors, particularly factor VIII or factor IX.

2. **Inheritance Pattern**: Haemophilia is known to be an X-linked recessive trait. This means that the gene responsible for haemophilia is located on the X chromosome.

3. **Carrier Female**: A carrier female has one normal X chromosome and one X chromosome with the haemophilia gene. Therefore, she does not exhibit symptoms of the disease but can pass the affected X chromosome to her offspring.

4. **Transmission to Male Progeny**: Males have one X and one Y chromosome (XY). If a carrier female passes on her X chromosome with the haemophilia gene to a male child, the male will express the condition because he does not have a second X chromosome to mask the effect of the recessive gene.

5. **Conclusion**: Therefore, haemophilia is transmitted from a normal carrier female to male progeny because it is an X-linked recessive trait. This explains why the condition is more commonly expressed in males than in females.

**Final Answer**: Haemophilia is transmitted from normal carrier female to male progeny because it is an **X-linked recessive trait**.

---