Can two type O parents have a child that is not type O?

No. Type O means the genotype is OO (ii), so each type O parent can only pass an O allele. Every child of two type O parents is therefore OO, or type O. This is one of the few blood type combinations that gives a single certain outcome, which is why it comes up so often in genetics problems.

Can an AB parent and an O parent have an AB or an O child?

No, neither is possible. The AB parent passes either an A or a B allele, and the O parent can only pass an O allele. So every child is AO (type A) or BO (type B). This AB by O cross is the classic example that a child can have a blood type different from both parents, and that AB and O children are ruled out.

Why are A and B called codominant?

Codominant means both alleles are fully expressed when present together, rather than one masking the other. A person with the AB genotype makes both the A antigen and the B antigen on their red blood cells and has blood type AB, showing both traits at once. This is different from the O allele, which is recessive to both A and B.

How is the Rh factor inherited?

The Rh factor is a separate gene from ABO, with Rh positive (the D allele) dominant over Rh negative (d). A positive person is DD or Dd, and a negative person is dd. Because it is a simple dominant and recessive gene inherited independently of ABO, you calculate it on its own and then combine it with the ABO result by multiplying the probabilities.

Can this calculator prove paternity?

No. Blood type can sometimes rule a person out as a possible parent when the child's type could not come from that pairing, but it can never prove parentage, because many people share the same blood type. Only DNA testing can confirm a biological relationship. Treat these results as genetics practice, not a paternity test.

Blood Type Inheritance Calculator (ABO + Rh), Free

Parent 1

ABO genotype

Rh genotype

Parent 2

ABO genotype

Rh genotype

Only know the blood type, not the genotype? Type A can be AA or AO, type B can be BB or BO, and Rh+ can be DD or Dd. Try each to see the full range.

Possible child blood types

The ABO Punnett square

How blood type inheritance works

Two independent genes set your blood type. The ABO gene has three alleles: A and B are codominant (both show up together as type AB), and both are dominant over the recessive O allele. So type A is AA or AO, type B is BB or BO, type AB is exactly AB, and type O is OO. The Rh gene is separate and simpler: Rh positive (D) is dominant over Rh negative (d). Because the two genes are inherited independently, you solve each with its own Punnett square and then multiply the probabilities to get a full type like A positive or O negative.

ABO genotypes and blood types

Blood type	Possible genotypes	Antigens on red cells
A	AA or AO	A
B	BB or BO	B
AB	AB	A and B (codominant)
O	OO	none

O is often written i, and the A and B alleles as I^A and I^B. The letters here are kept simple, but the genetics are identical.

FAQ

Can two type O parents have a non-O child?
No. Both are OO, so they can only pass O, and every child is type O.

Can AB and O parents have an AB or O child?
No. Children are type A (AO) or type B (BO) only. This is the classic case where kids differ from both parents.

Why are A and B codominant?
Both are fully expressed together: an AB person makes both A and B antigens, showing both traits at once.

How is Rh inherited?
As a separate dominant gene: Rh+ (D) is dominant over Rh− (d). Solve it on its own, then multiply with the ABO result.

Can this prove paternity?
No. It can sometimes rule a pairing out, but never prove it. Only DNA testing confirms parentage.