How is blood type inherited?

Blood type is determined by three alleles: A, B, and O. A and B are codominant; O is recessive. Each parent passes one allele to the child. For example, type A can have genotype AA or AO, so an A parent and an O parent can have children with type A or type O.

Can two type A parents have a type O child?

Yes — if both parents carry the AO genotype (heterozygous A). In that case, there is a 25% chance of an OO child (type O). Two AA parents cannot have a type O child.

What blood type is the universal donor?

O negative (O-) is the universal red blood cell donor because it lacks A, B, and Rh antigens. AB positive (AB+) is the universal recipient.

Can blood type determine paternity?

Blood type can rule out paternity but not confirm it. Certain parent-child combinations are genetically impossible (e.g., two O parents cannot have an AB child). DNA testing is required for conclusive paternity results.

How does Rh factor inheritance work?

Rh+ is dominant over Rh-. Two Rh- parents always produce Rh- children. If at least one parent is Rh+, the child can be Rh+ or Rh-. If both are Rh+, there is still a 25% chance of an Rh- child if both carry the recessive Rh- allele.

Blood Type Calculator

Predict possible child blood types from parents using Punnett square genetics. Check donation compatibility and paternity blood type consistency.

Parent 1 Blood Type

Parent 1 Rh Factor

Parent 2 Blood Type

Parent 2 Rh Factor

Possible Child Blood Types

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Rh+ Probability —

Most Likely Type —

Universal Donor / Recipient —

Extended More scenarios, charts & detailed breakdown ▾

Parent 1 Blood Type

Parent 1 Rh Factor

Parent 2 Blood Type

Parent 2 Rh Factor

Possible Child Blood Types

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Probability Type A —

Probability Type B —

Probability Type AB —

Probability Type O —

Rh+ Probability —

Professional Full parameters & maximum detail ▾

Parent 1 Blood Type

Parent 1 Rh

Parent 2 Blood Type

Parent 2 Rh

Parent 1 Genotype (if known)

Parent 2 Genotype (if known)

ABO Blood Type Probabilities

Probability Type A —

Probability Type B —

Probability Type AB —

Probability Type O —

Rh Factor

Rh+ Probability —

Rh- Probability —

Genotype Details

Parent 1 Possible Genotypes —

Parent 2 Possible Genotypes —

Can Child Be Universal Donor (O-)? —

Can Child Be Universal Recipient (AB+)? —

How to Use This Calculator

Select Parent 1 and Parent 2 blood types (A, B, AB, or O) and Rh factors (+/-).
The calculator uses Punnett square genetics to show all possible child blood types with probabilities.
Use the Compatibility tab to see who each blood type can donate to or receive from.
Use the Paternity Check tab to test whether a combination is genetically consistent.

Formula

ABO genotypes: A = AA or AO | B = BB or BO | AB = AB | O = OO
Cross all parental allele combinations to find child probabilities.
Rh+: dominant | Rh-: recessive (two Rh- parents → always Rh- child)

Example

Example: Parent 1 type A (AO) × Parent 2 type B (BO) = 25% A, 25% B, 25% AB, 25% O — all four blood types are possible.

Frequently Asked Questions

Blood type is determined by three alleles: A, B, and O. A and B are codominant; O is recessive. Each parent passes one allele to the child. For example, type A can have genotype AA or AO, so an A parent and an O parent can have children with type A or type O.
Yes — if both parents carry the AO genotype (heterozygous A). In that case, there is a 25% chance of an OO child (type O). Two AA parents cannot have a type O child.
O negative (O-) is the universal red blood cell donor because it lacks A, B, and Rh antigens. AB positive (AB+) is the universal recipient.
Blood type can rule out paternity but not confirm it. Certain parent-child combinations are genetically impossible (e.g., two O parents cannot have an AB child). DNA testing is required for conclusive paternity results.
Rh+ is dominant over Rh-. Two Rh- parents always produce Rh- children. If at least one parent is Rh+, the child can be Rh+ or Rh-. If both are Rh+, there is still a 25% chance of an Rh- child if both carry the recessive Rh- allele.

Related Calculators

Sources & References (5) ▾

Landsteiner K — Zur Kenntnis der antifermentativen, lytischen und agglutinierenden Wirkungen des Blutserums und der Lymphe. Zbl Bakt. 1900;27:357-362 (original ABO discovery) — NCBI / Historical
AABB — Technical Manual, 20th ed. (2020) — ABO and Rh blood group genetics — AABB
Reid ME & Lomas-Francis C — The Blood Group Antigen FactsBook, 3rd ed. (2012) — Academic Press / Elsevier
WHO — Blood safety and availability — Blood groups — World Health Organization
Dean L — Blood Groups and Red Cell Antigens (NCBI Bookshelf, 2005) — NCBI