Which of the following conditions is true for codominance?

If two individuals with $AB$ blood group marry and have a large number of children,the children show $A$,$AB$,and $B$ blood groups in a ratio of $1:2:1$. Since proteins of both $A$ and $B$ types are present in individuals with $AB$ blood group,this is an example of:

Formation of $AB$ type of blood group in humans is due to . . . . . . inheritance.

When two genes with independent expression are present together, they both express their characteristics, and when they are separate, they express their individual characteristics. This phenomenon is observed in which of the following?

In which of the following is codominance observed?

In the context of the $ABO$ blood group system,what happens when both alleles $I^A$ and $I^B$ are present together?