Explain thalassemia.

In pedigree analysis, symbol given for sex unspecified is

Person whose father is colourblind marries a lady whose mother is daughter of a colourblind man. Their children will be

Give scientific reasons : The human male never passes on the gene for haemophilia to his son.
 

Haemophilic female marries normal male, the theoretical ratio of their offsprings regarding haemophilia will be

Assertion : Haemophilia is a recessive sex linked disease.

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