Haemophilia is caused by

The correct option is Genetic mutation.

Step-by-step Explanation:

1. Understanding Haemophilia:
Haemophilia is a rare inherited bleeding disorder in which the blood does not clot normally. People with haemophilia lack or have low levels of certain proteins called clotting factors (such as Factor VIII or Factor IX) that work with platelets to stop bleeding after an injury.

2. Underlying Cause:
The production of clotting factors is controlled by specific genes. Haemophilia is caused by a genetic mutation (an alteration in the DNA sequence) in one of these genes, which is located on the X chromosome. Because it is an X-linked recessive disorder, it primarily affects males, while females are typically carriers.

3. Evaluating the Options:
- Bacteria: Bacteria cause infectious diseases (like tuberculosis or cholera), not genetic disorders.
- Virus: Viruses cause viral infections (like influenza or COVID-19), not inherited conditions.
- Genetic mutation: This is the correct cause, as alterations in the genes responsible for producing clotting factors lead to the disease.
- Cause unknown: The genetic basis and inheritance pattern of haemophilia are well-understood by science.