Which of the following is a trait of X-linked recessive?

The correct answer is Haemophilia.

To understand why haemophilia is the correct option, let's break down the genetic characteristics of X-linked recessive traits and examine the options provided:

1. Understanding X-Linked Recessive Inheritance:
X-linked recessive inheritance refers to genetic conditions caused by a mutation in a gene on the X chromosome.
- Males have one X and one Y chromosome (XY). Because they only have one X chromosome, a single mutated gene on that chromosome is sufficient to cause the condition.
- Females have two X chromosomes (XX). For a female to express an X-linked recessive trait, she must inherit two copies of the mutated gene (one from each parent). If she inherits only one mutated copy, she is typically an unaffected carrier.
Consequently, X-linked recessive traits are much more commonly expressed in males than in females.

2. Analysing the Options:
- Albinism: Most common forms of albinism, such as Oculocutaneous Albinism (OCA), are inherited in an autosomal recessive pattern (affecting genes on non-sex chromosomes), not X-linked.
- Huntington's disease: This is a progressive neurological disorder inherited in an autosomal dominant pattern.
- Haemophilia: Haemophilia (specifically Haemophilia A and Haemophilia B) is a classic example of an X-linked recessive disorder. It is caused by mutations in genes located on the X chromosome that code for essential blood-clotting factors (Factor VIII in Haemophilia A and Factor IX in Haemophilia B). Because of this X-linked inheritance pattern, the disease primarily affects males, while females are usually carriers.

Therefore, haemophilia is the correct trait representing an X-linked recessive mode of inheritance.