In which of the following is the expression of both alleles of a gene pair in a heterozygous condition observed?

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:

The $AB$ blood group exhibits which of the following phenomena?

In cattle,when a cross results in offspring with roan (spotted) coat color,which of the following phenomena is demonstrated?

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