Tukuk-OS🩸 Blood Type Punnett
ℹ️ What this tool does & how it works
ABO blood is three alleles with two dominances: A and B are codominant, both dominant over O. Phenotype hides genotype — group A is AA or AO — so this page takes the genotypes and lays out the actual 2×2 square. The famous punchlines fall out of it: two A parents can have an O child, and an A × B couple can have any of the four groups.
Codominance, dominance, and the carrier trick
Mendel\u2019s pea colours showed dominance; ABO adds codominance on top. An AO person types as A because the A allele builds an A antigen on every red cell and the O allele builds nothing — dominance is a statement about what the surface displays, not what the DNA carries. An AB person displays both antigens side by side, which is why A and B are called codominant: neither hides the other. The carrier mechanic is why two group-A parents can have an O child (AO × AO gives 25% OO) and why group O appears suddenly in family trees — the genotype was invisible for a generation, not absent. The 2×2 square above is exactly the tool Reginald Punnett invented in 1905 for this arithmetic.