Haemophilia is a genetic disorder of coagulation seen only in males. It is transmitted as
**Core Concept**
Haemophilia is a genetic disorder characterized by a deficiency in blood clotting factors, leading to prolonged bleeding. It is caused by mutations in genes responsible for coagulation, which are located on the X chromosome.
**Why the Correct Answer is Right**
Haemophilia is inherited in an X-linked recessive pattern, meaning the genes responsible for the disorder are located on the X chromosome. Females have two X chromosomes, one inherited from each parent, and are typically carriers of the mutated gene. Males, having only one X chromosome, are more likely to express the disorder if they inherit the mutated gene. In females, the presence of a second X chromosome often compensates for the mutated gene, making them less likely to develop symptoms.
**Why Each Wrong Option is Incorrect**
**Option A:** X-linked dormant is not a recognized pattern of inheritance. While some genetic disorders may exhibit "variable expressivity," Haemophilia's inheritance pattern is well-established as X-linked recessive.
**Option B:** Y-linked dormant is incorrect because the Y chromosome does not carry the genes responsible for Haemophilia. The disorder is linked to the X chromosome.
**Option D:** Autosomal recessive is incorrect because Haemophilia is specifically linked to the X chromosome, not an autosomal chromosome.
**Clinical Pearl / High-Yield Fact**
Haemophilia A and B are the two most common forms of the disorder, caused by deficiencies in clotting factors VIII and IX, respectively. Understanding the X-linked recessive inheritance pattern is crucial for genetic counseling and family planning in affected families.
**✓ Correct Answer: C. X-linked recessive**