Haemophilia is a genetic disorder, which is due to the mutation (change in structure) of the gene responsible for producing Factor VIII or Factor IX. Haemophilia is also typically hereditary, meaning it is passed down from one generation to the next through these “defective” (mutated) genes. Specifically, the male inherits the mutated gene from his mother. This is because the gene is located on chromosome X of the gender. What exactly does this mean?

Genes are located in chromosomes. Individuals inherit one chromosome from their father and one chromosome from their mother.

The gender of a person is determined by the sex chromosomes. These are the X and Y chromosomes. Females have two X chromosomes (ΧΧ) while males have an X chromosome and a Y chromosome (ΧΥ).

Thus, each male has only one X chromosome. If the boy then inherits from his mother the X chromosome in which the haemophilia gene is located, then this boy will develop haemophilia.