ABO blood groupsSpec 3.17B
The ABO blood group is controlled by a single gene with multiple alleles: more than two alleles of the same gene. There are three alleles, written here as IA, IB and IO. A person inherits two, one from each parent.
IA and IB are codominant: if both are present, both are expressed in the phenotype. IO is recessive to both.
| Phenotype (blood group) | Possible genotypes |
|---|---|
| A | IA IA or IA IO |
| B | IB IB or IB IO |
| AB | IA IB |
| O | IO IO |
Parents with group A and group B
A mother is IA IO and a father is IB IO. What blood groups could their children have?
- Mother's gametes: IA or IO. Father's gametes: IB or IO.
- Possible children: IA IB, IA IO, IB IO and IO IO.
Answer: Group AB, A, B and O, each with a 1 in 4 (25%) probability.