ABO Blood Group Summary Table
| Blood Group | Genotype(s) | RBC Antigen | Plasma Antibody | Can Donate To | Can Receive From |
|---|---|---|---|---|---|
| A | or i | A | Anti-B | A, AB | A, O |
| B | or i | B | Anti-A | B, AB | B, O |
| AB | A and B | None (Universal Recipient) | AB only | A, B, AB, O | |
| O | ii | None | Anti-A and Anti-B (Universal Donor) | A, B, AB, O | O only |
Clinical Applications
- Blood Transfusion: Universal donor (O) can donate to any recipient because O RBCs carry no antigens. Universal recipient (AB) can receive from any donor because AB plasma carries no antibodies.
- Parentage/Forensic Testing: Blood group genetics can exclude parentage. Example: Two AB parents cannot have an O child; an AB parent cannot produce an O child with any partner.
- Haemolytic Disease of Newborn (HDN): Can occur when mother's ABO antibodies cross the placenta and attack fetal RBCs (less severe than Rh incompatibility but possible).
NEET Problem Types
- Given parents' blood groups → find possible offspring blood groups
- Given child's blood group → determine which parents are excluded
- Identify genotype from blood group + parental information (use grandfather's blood group to determine which allele the parent inherited)
Key Cross: i × i (A × B, both heterozygous)
All four blood groups possible in offspring in equal proportions:
- (AB) = 1/4
- i (A) = 1/4
- i (B) = 1/4
- ii (O) = 1/4