Haemophilia is

The correct option is X – linked.

Detailed Explanation:

Haemophilia (often spelled hemophilia) is a mostly inherited genetic disorder that impairs the body's ability to make blood clots, a process needed to stop bleeding. This results in people bleeding for a longer time after an injury, easy bruising, and an increased risk of bleeding inside joints or the brain.

The genes responsible for producing coagulation factors VIII (8) and IX (9), which are crucial proteins in the blood clotting cascade, are located on the X chromosome. Because the mutated gene is located on the X chromosome, the inheritance pattern of haemophilia is classified as X-linked (specifically, X-linked recessive).

Humans have two sex chromosomes: females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
- In males, who have only one X chromosome, a single altered copy of the gene on their X chromosome is sufficient to cause the condition.
- In females, who have two X chromosomes, a mutation would generally have to occur on both copies of the gene to cause the disorder. If a female inherits only one mutated X chromosome, she becomes a carrier of haemophilia but typically does not show severe symptoms because the normal X chromosome compensates for the defective one.