Blood Type Inheritance: What Your Parents' Types Tell You
Interactive Punnett calculator plus a complete guide to ABO and Rh inheritance. Updated April 2026.
Blood Type Inheritance Calculator
Mother's blood type:
Father's blood type:
Possible child blood types:
Percentages are based on possible allele combinations. Actual probability depends on parents' specific genotypes. This is a simplified model - genetic testing is required to determine exact genotypes.
How ABO Blood Type Is Inherited
ABO blood type is controlled by a single gene with three alleles: I^A (produces A antigen), I^B (produces B antigen), and i (produces neither antigen). Every person carries exactly two copies - one inherited from each parent.
A and B alleles are codominant: if you carry one of each, both express and you are type AB. The i allele is recessive: it only expresses when you carry two copies (ii genotype), giving you type O. This explains why:
| Blood type | Possible genotypes | What this means |
|---|---|---|
| A | I^A I^A or I^A i | Two A alleles, or one A and one O |
| B | I^B I^B or I^B i | Two B alleles, or one B and one O |
| AB | I^A I^B | One A allele and one B allele (always) |
| O | ii | Two O alleles (always) |
Because A-type and B-type people can be heterozygous (carrying a hidden O allele), their children can be O-type. But AB-type people always pass either an A or a B allele - never an O - so two AB parents cannot have an O child.
How Rh Factor Is Inherited
The Rh-D gene has two common versions: D (dominant, produces Rh-D antigen = Rh-positive) and d (recessive, produces no Rh-D antigen). Rh-positive individuals carry at least one D allele (DD or Dd genotype). Rh-negative individuals carry two d alleles (dd genotype).
Because D is dominant, having even one D allele results in Rh-positive blood. This means:
- Two Rh-negative parents (dd x dd) always produce Rh-negative children
- An Rh-positive parent can be DD (homozygous) or Dd (heterozygous carrier)
- If one Rh-positive parent is Dd and the other is Rh-negative (dd), each child has a 50% chance of being Rh-negative
- This is why Rh-negative children can be born to one Rh-positive parent
Common Parental Combinations
Possible child types: O+, O-
Both parents are O-type. Child will always be O. Rh depends on parent genotypes.
Possible child types: A+, A-, B+, B-, AB+, AB-, O+, O-
Wide range of possible outcomes. Both parents could carry O or Rh-negative alleles.
Possible child types: A+, A-, B+, B-
No O children (AB parent always passes A or B). No O-type possible.
Possible child types: A+, A-, O+, O-
Father may carry O and/or Rh- alleles. Child could be A or O, positive or negative.
Can Parents with O Blood Have an AB Child?
No - under normal genetics. O-type individuals have the genotype ii (two recessive O alleles). They have no A or B allele to pass to a child. An AB child requires one A allele from one parent and one B allele from the other. Neither O-type parent can supply either.
There is one extremely rare exception: the Bombay phenotype. People with Bombay phenotype (h/h) lack the H antigen and appear to be type O in standard testing - but they may actually carry A or B alleles that are simply not expressed. If both parents are Bombay phenotype carriers, their child could theoretically have AB-type blood despite parents appearing to be O. This is vanishingly rare.
In standard genetics: O + O = O children only. AB children from two O parents are not possible.
Bombay phenotype explained +Blood Type and Paternity Testing
Blood type can exclude paternity in some cases. If a child has blood type O and the claimed father is AB, paternity can be excluded - because an AB parent always passes either A or B, never O. Similarly, if a child is AB and one parent is O, the O parent cannot be the biological parent (under standard genetics).
However, blood type cannot confirm paternity. Many men could potentially be the father of a child with a given blood type. For legal, medical, or personal paternity determination, DNA testing is required. DNA testing can establish paternity with greater than 99.9% probability.