$ABO$ blood group is a good example of:

In which of the following phenomena can both dominance and codominance be observed?

As per the $ABO$ blood grouping system,the blood group of the father is $B^{+}$,the mother is $A^{+}$,and the child is $O^{+}$. Their respective genotypes can be:
Choose the most appropriate answer from the options given below:
$A. I^Bi / I^Ai / ii$
$B. I^BI^B / I^AI^A / ii$
$C. I^AI^B / iI^A / I^Bi$
$D. I^Ai / I^Bi / I^Ai$
$E. iI^B / iI^A / I^AI^B$

$ABO$ blood groups in humans are controlled by the gene $I$. It has three alleles: $I^A, I^B$ and $i$. Since there are three different alleles, six different genotypes are possible. How many phenotypes can occur?

Mother is homozygous for blood group $B$,and father has blood group $A$ (genotype unknown). Therefore,the possible blood groups in the progeny are:

Define/Explain: Multiple Allelism.