Question

Haemophilia does not occur in women because

• A. It is autosomal recessive.
• B. Women have to be homozygous, which is fatal.
• C. They have only one X chromosome.
• D. They are more resistant to this disorder.

Answer 1

The correct option is B Women have to be homozygous, which is fatal.

Haemophilia is mostly expressed in the male who inherit it from affected or carrier mothers which mean that it is inherited in sex-linked manner, not in an autosomal manner. Only affected fathers and affected or carrier mothers can have affected daughters which mean that the trait is recessive. This is because females have two copies of X-chromosomes (option C is wrong) and need the recessive trait to be present in two copies to express it. This makes option A wrong. A homozygous recessive female express the disease but they do not survive due to impaired ability or inability of blood clotting which causes heavy blood loss even in the case of small injury. This makes option D wrong and option A correct.