Sickle-cell anaemia happens due to …$A$… mutation in which …$B$… of haemoglobin is affected.

Fill the correct option for $A$ and $B$

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

In a sickle cell anaemia glutamic acid is replaced by valine, which the following codes for glutamic acid ?

A man whose father was colour blind marries a woman who had a colour blind mother and normal father. What percentage of male children of this couple will be colour blind?

Colour blindness results from