Phenylketonuria is a genetic disorder due to a defect in the metabolism of which of the following?

Assertion : Persons suffering from haemophilia fail to produce blood clotting factor $VIII$.
Reason : Prothrombin producing platelets in such persons are found in very low concentration.

If both parents are carriers for thalassaemia,which is an autosomal recessive disorder,what are the chances of pregnancy resulting in an affected child?

Alkaptonuria is a condition in which

$A$ haemophilic woman marries a normal man,then:

Colour blindness is