Haemophilia is categorised as Mendelian disorders because they occur by mutation in a single gene. Its mode of inheritance follows the principles of Mendelian genetics. Mendelian disorders can be

• autosomal dominant (muscular dystrophy)
• autosomal recessive (thalassaemia)
• *** linked (haemophilia)

Symptoms of Haemophilia

• Person suffering from this disease does not develop a proper blood clotting mechanism.
• A haemophilic patient suffers from non-stop bleeding even on a simple cut, which may lead to death.

Pattern of Inheritance of Haemophilia:
Haemophilia is an X-linked genetic disorder. Compared to females, males have higher chances of getting affected because females have XX chromosomes while males have only one X with Y chromosome. Thus, for a female to get affected by haemophilia, she has to have the mutant gene on both the X chromosomes while males can be affected if they carry it on the single X chromosome.
Conditions for haemophilia:
XY; XX: Normal
X^hY: Haemophilic
X^hX: Carrier
X^hX^h: Haemophilic
Let us assume that a carrier female (X^hX) is married to a normal male.