Select parental genotypes to display child blood type probabilities via Punnett square in real time. Calculate ABO and Rh factor independent inheritance according to Mendel's laws.
The parents' allele pairs change periodically, and the four possible offspring combinations drop into a 2×2 square to calculate the probabilities of blood types A, B, AB, and O. IA and IB are codominant, while i is recessive (O). Example: AO×BO → A 25%, B 25%, AB 25%, O 25%.
💬 Deep Dive into Blood Type Genetics 'Why'
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How are blood types passed from parents to children? Can two A-type parents have an O-type child?
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Yes, that's a common question. ABO blood type is determined by three alleles: IA, IB, and the recessive i. Each person has two alleles. If an A-type person has the genotype IA i, they can pass i to their child. If the other parent also carries i, the child can be ii (type O). So even if someone looks like type A, they might be carrying a hidden i.
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So is it true that an AB × O couple can never have an AB or O child?
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That's correct. The AB genotype is always IAIB, and O is always ii. In the Punnett square, all four squares are either IAi or IBi, meaning only type A or type B children are possible. If an AB × O couple had an AB child, that would be genetically inconsistent and would require checking parentage. Historically, this was actually used for paternity testing.
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What does it mean that a B × A couple can have all four blood types?
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That happens when the father is IBi (type B) and the mother is IAi (type A). The Punnett square gives IAIB (AB), IAi (A), IBi (B), and ii (O), each with a 25% probability. This is a classic textbook example in genetics. You can check it in the simulator by selecting the preset for this combination.
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What is the Rh factor? I don't hear about it much in Japan.
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It's about whether the Rh (D) antigen is present on red blood cells: positive (+) if present, negative (-) if absent. Only about 0.5% of Japanese people are Rh-negative, so it's rarely discussed in daily life, but in Western countries it's around 15%. If an Rh-negative woman becomes pregnant with an Rh-positive fetus, her body can produce Rh antibodies, which may attack the red blood cells of a future fetus, causing hemolytic disease of the newborn. That's why Rh factor is as important as ABO type in blood transfusions and pregnancy management.
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Is it true that blood type determines personality?
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There is no scientific basis for that. Large-scale psychological studies have repeatedly shown no statistically significant correlation between blood type and personality. In fact, comparing research from Japan, Western countries, China, and South Korea, a weak correlation is only detected in societies where blood type personality theory is widespread. This can be explained by self-fulfilling prophecy (acting according to what you believe) and confirmation bias. Blood type is genetically interesting, but it has nothing to do with determining personality.
Frequently Asked Questions
How is ABO blood type inherited?
ABO blood type is determined by three alleles (IA, IB, i) at a single gene locus. IA and IB are codominant (both expressed) and dominant over i (i is recessive). Each person inherits one allele from each parent, and the combination determines the blood type. Phenotype-genotype correspondence: Type A (IAIA or IAi), Type B (IBIB or IBi), Type AB (IAIB), Type O (ii).
Can an AB × O couple have an O or AB child?
No. The AB genotype is always IAIB, and O is always ii. The only possible combinations from this cross are IAi (type A) and IBi (type B). Therefore, an AB × O couple can only have type A or type B children. This was used for paternity testing before DNA analysis.
Which parental combination can produce children of all four blood types?
When the father is IBi (heterozygous B) and the mother is IAi (heterozygous A), or vice versa. The Punnett square yields IAIB (AB), IAi (A), IBi (B), and ii (O), each with a 25% probability. You can verify this using the simulator's preset 'B × A: All 4 types!'.
What happens if an Rh-negative person receives a blood transfusion?
If an Rh-negative person receives Rh-positive blood, their body may produce Rh antibodies (anti-D) (sensitization). On a second transfusion of Rh-positive blood, the antibodies react, destroying the transfused red blood cells (hemolytic reaction). The first transfusion usually causes no major reaction, but subsequent transfusions carry a risk of severe adverse effects. Therefore, Rh type confirmation is essential for blood transfusions, organ transplants, and pregnancy management.
Can blood type change?
In principle, blood type does not change throughout life, but it can change to the donor's type after a bone marrow transplant (since hematopoietic stem cells produce red blood cells that determine blood type). Additionally, blood type antigens may weaken or temporarily appear different in hematopoietic diseases like leukemia. Rare blood type variants, such as A type mimicking B type (Bm type), also exist.
Select the ABO genotype for each parent (AA, AO, BB, BO, AB) from the dropdown menus
Choose the Rh factor for each parent (positive or negative)
Click "Generate Punnett Square" to display all possible allele combinations
Review the offspring probability table showing blood type percentages and phenotypic outcomes
Worked Example
Consider a cross between two heterozygous parents: Mother genotype AO, Rh positive (Rh+/−) and Father genotype BO, Rh positive (Rh+/−). The Punnett square generates 16 possible combinations. ABO outcomes: 25% Type A (AA or AO), 25% Type B (BB or BO), 25% Type AB, 25% Type O (OO). Rh factor: 75% Rh positive offspring, 25% Rh negative. Therefore, a child has 18.75% probability of Type A positive blood, 18.75% Type B positive, and 6.25% Type O negative.
Practical Notes
AB parents cannot produce Type O children since AB genotype lacks the recessive O allele—useful for paternity screening in clinical genetics
Two Rh negative parents (−/−) will always produce Rh negative children; Rh incompatibility during pregnancy requires RhoGAM prophylaxis in obstetrics
Codominance of A and B alleles means AB individuals express both antigens on red blood cells, determining universal recipient status for transfusion medicine