Question

Why is blood group AB considered as a universal recipient?

Answer 1

The word universal means done by all people or groups or applicable in all the cases and the term recipient means a person receiving or capable of receiving something.
During blood transfusion, any blood can’t be used. Before blood transfusion, the blood of the donor and recipient should be carefully matched to avoid any serious problems.

Complete answer:
Blood group AB is considered as the universal recipient because individuals having blood group AB can receive blood from persons with AB as well as the other groups of blood.
ABO blood grouping is based on the presence of two surface antigens A and B on the RBC's surface.
Plasma of blood contains two antibodies anti-A and anti-B.
AB blood group people have both A and B antigen on their RBC's surface and they don’t possess any antibodies in their plasma. This makes them suitable to receive blood from any blood group.
Before blood transfusion, blood of donor and recipient are carefully matched because if there will be any mistake it can lead to severe problems and can even be fatal. If a different blood group is transferred into the recipient body it causes antigen antibody reactions causing clumping and destruction of RBC. It can lead to organ failures and in some cases it can be fetal too.

Note:
BO blood groups in humans are controlled by the gene I. The gene I has three alleles IA, IB and i.
IA and IB alleles are codominant with each other, i.e., when allele IA And IB are present together they both express their own types of sugar.
IA and IB are completely dominant over i allele.