1. ABO group is divided into four groups
2. A group consists of antigen A and antibody B
3. Group B consists of antigen B and antibody A
4. Group AB contains antigens A and B, but no antibodies
5. Group O has no antigens, but has antibodies A and B
6. It is called universal recipient as it can accept blood from all groups in group AB
7. O group is called universal donor as it can give blood to all groups