Which principle is demonstrated by a cross in which the $F_1$ generation resembles both parents?

In heterozygous condition,the individual expression of both the alleles in the phenotype is exemplified by

Which idea is depicted by a cross in which the $F_1$ generation resembles both the parents?

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:

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

Write a short note on co-dominance.