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Computes the possible ABO/Rh blood types of a child given both parents' blood types, using standard Mendelian genetics: the ABO gene has three alleles (A and B are codominant, O is recessive), and Rh(D) is a separate dominant/recessive trait that assorts independently. Because a visible phenotype (like "A") does not reveal whether the underlying genotype is homozygous or heterozygous, this calculator applies the standard simplifying assumption used in introductory genetics teaching: each possible genotype is treated as equally likely, then a standard Punnett-square cross is applied. This is a genetics/probability calculation, not a medical or paternity determination, and does not account for rare exceptions like the Bombay phenotype. For general reference and educational purposes only.
How it works
Select both parents' ABO/Rh blood types. The tool enumerates the possible genotypes behind each phenotype, crosses them using a standard Punnett square, and reports the probability of each possible child blood type.
- Enter parent 1's blood type.
- Enter parent 2's blood type.
- Click Calculate to see your results.
Examples
O+ x O+
Since O is fully recessive, both parents' ABO genotype must be OO, so the child is 100% type O for ABO. For Rh, since "+" could be homozygous or heterozygous, there is roughly a 6.25% chance of an Rh-negative child even when both parents are Rh-positive.
Who should use it
- Learning Mendelian genetics and Punnett squares.
- Biology classroom demonstrations.
Industry applications
- Biology and genetics education
- General science curriculum support
Advantages
- Covers all 8 standard ABO/Rh blood types.
- Shows a full probability distribution, not just one possible answer.
Limitations
- Assumes equal genotype likelihood for ambiguous phenotypes (a simplification, not true population genotype frequency).
- Does not account for rare exceptions like the Bombay phenotype.
Common mistakes to avoid
- Assuming a phenotype like "A+" maps to one single genotype — it can represent multiple possible genotypes.
- Treating the output as a certainty rather than a probability distribution.
Best practices
- Use this as a genetics learning tool, not as evidence in any real-world paternity or medical question.
Tips
- Try entering both parents as the same heterozygous-possible type (e.g. A+ and A+) to see how a recessive combination can still appear in a child.