Explain thalassemia.

Give scientific reasons : The product of phenylalanine catabolism excreted in the urine in phenylketonuria.
 

A normal woman, whose father was colour-blind is married to a normal man. The sons would be

Assertion : Haemophilia is a recessive sex linked disease.

Reason : Haemophilia occurs due to mutation of a structural gene on chromosome $15$.

Colour blindness is caused by a single