Mutation

not necessary, if dda registered directly son it is valid onle dont worry

But DDA does not register. Property is registered by sub registrar office after charging stamp duty. DDA only gives permission so that it can be registered at the sub registrar office.

Another point,  father got the plot though draw of lottery and not as direct purchase.

dont worry, if dda registert\ed through sub-regsistrar is valid one.

any form lottery or purchase it is same validity.

if dda accepted to register the sale deed  through sub-register it is valid one.

If mutation has already been made in son's name in DDA records, he can also get the plot registered directly in his own name. There is no need for registration in the name of the father, as the plot already stands mutated in the name of his son.

Thanx for your considered reply!