Blood Groups Questions

A person with unknown blood group under ABO system, has suffered much blood loss in an accident and needs immediate blood transfusion. His one friend who has a valid certificate of his own blood type, offers for blood donation without delay. What would have been the type of blood group of the donor friend?

The most popularly known blood grouping is the $\text{ABO}$ grouping. It is named $\text{ABO}$ and not $\text{ABC}$, because "O" refers to having:

$\text{ABO}$ blood groups in humans are controlled by the gene $I$. It has three alleles—$I^A,I^B$ and $i$. How many phenotypes can occur?

A certain road accident patient with unknown blood group needs immediate blood transfusion. His one doctor friend at once offers his blood. What was the blood group of the donor?