Blood groups and RH system:

There are 4 types of blood groups:  

• A, B, AB and O. Gene I controls these blood groups. This gene I has 3 alleles (I^A , I^B   , and I^O).
• I^A  and I^B  alleles produces antigens A and B respectively. Antigens are present on surface of RBCs.
•  Alleles I^A and   I^B produces (anti-B) and (anti-A) respectively. Antibodies are present in plasma of blood.
• Both I^A and I^B alleles form their respective type of sugar on RBCs molecules but I^O  cannot forms any type of sugar.

Blood groups	Antigen(on surface)	Antibody(in plasma)	Alleles
A	A	Anti-B	IA   IA , IA  IO
B	B	Anti-A	IB   IB , IB   IO
AB	A & B	None	IA   IB
O	None	Anti-A & anti-B	IO   IO

Blood group	Possible recipient	Possible donor
A	A, AB	O, A
B	B, AB	O, B
AB	AB	AB, O,A,B	Universal recipient
O	A, B, AB, O	O	Universal donor

RH (rhesus system):

 The human beings whose RBCs contain RH antigen on their surface are called RH⁺ and those who don’t have are called RH^- . If father is RH negative and mother is RH positive and mother first becomes pregnant with RH negative baby. Then mother becomes sensitive as some RBCs of RH negative antigens goes into mothers blood. Due to this, mother body starts producing anti-RH antibodies against it. But if she becomes pregnant again with RH negative child, then the anti-RH antibodies produced in her body affects the fetus developing and kill the RBCs of fetus. This disease of fetus is called hemolytic disease of newborn.