What is the phenomenon called where factors produce independent effects in their heterozygous condition?

If two persons with $AB$ blood group marry and have a sufficiently large number of children,these children could be classified as $A$ blood group : $AB$ blood group : $B$ blood group in $1 : 2 : 1$ ratio. Modern techniques of protein electrophoresis reveal the presence of both $A$ and $B$ type proteins in $AB$ blood group individuals. This is an example of:

In the $ABO$ blood grouping system,which of the following is an example of co-dominance?

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

What will be the phenotypic ratio of the offspring when a roan-colored cow is crossed with a white bull?

In shorthorn cattle,genes for red $(R_1)$ and white $(R_2)$ coat colour occur. Crosses between red $(R_1R_1)$ and white $(R_2R_2)$ produced $(R_1R_2)$ roan. This is an example of