Multiply each parent’s probability of passing on a given allele together to find the probability of each possible offspring genotype combination.
Punnett Square Calculator
Offspring genotype and phenotype probabilities from a genetic cross — a single gene (monohybrid), up to three independent genes, or ABO/Rh blood type.
Calculating Genetic Cross Probabilities
A Punnett square works out the probability of each possible offspring genotype and phenotype from a genetic cross between two parents, and this calculator covers a single gene (monohybrid cross), up to three independent genes at once, and the real-world ABO/Rh blood type inheritance pattern. It covers searches like Punnett square calculator, monohybrid cross calculator, dihybrid cross calculator, and blood type calculator genetics.
How the Punnett Square Calculator Works
Formula (Single Gene)
P(genotype) = P(allele from parent 1) × P(allele from parent 2), summed across all combinations giving that genotype
Formula (Multiple Independent Genes)
P(combined outcome) = P(gene 1 outcome) × P(gene 2 outcome) × P(gene 3 outcome), since independent genes’ probabilities multiply
Worked Example (Single Gene)
Two heterozygous (Aa) parents crossed: Each parent has a 50% chance of passing A and 50% chance of passing a. P(AA) = 0.5 × 0.5 = 25%. P(Aa) = (0.5 × 0.5) + (0.5 × 0.5) = 50%. P(aa) = 0.5 × 0.5 = 25%. P(dominant phenotype) = P(AA) + P(Aa) = 75%.
Worked Example (Two Independent Genes)
Two dihybrid (AaBb × AaBb) parents: P(recessive at gene A) = 0.5 × 0.5 = 25%, and the same for gene B. P(recessive at both genes) = 25% × 25% = 6.25%.
Why the Blood Type Mode Is Scientifically Accurate, Not Just a Teaching Model
The single-gene and multi-gene modes model simple dominant/recessive inheritance for illustration — real traits like eye color and hair color are influenced by multiple genes and other factors, so they don’t actually follow a simple one- or few-gene Punnett square, and should be treated as a simplified teaching example rather than a real prediction. The blood-type mode is different: it reflects the actual, well-established ABO/Rh inheritance pattern, assuming the ABO and RhD genes assort independently, which is scientifically accurate.
Frequently Asked Questions
Can this calculator predict a baby’s eye color?
No — eye color is influenced by multiple genes and other factors, not a single dominant/recessive gene pair, so the single-gene mode is only a simplified teaching illustration and not an accurate real-world prediction for traits like eye or hair color.
Is the blood type prediction mode actually accurate?
Yes — ABO and Rh blood type inheritance follows a well-established, scientifically accurate genetic pattern, assuming the ABO and RhD genes assort independently, which is generally the case, making this mode reliable for predicting possible offspring blood types from parental genotypes.
What does AO genotype mean for blood type?
AO means one A allele and one recessive O allele — since A is dominant over O, a person with AO genotype has type A blood, but can still pass on the O allele to offspring, which is why blood type inheritance sometimes surprises parents who are both type A or type B.
Does this calculator predict any health condition or disease risk?
No — none of the modes in this calculator predict any health condition; the single-gene and multi-gene modes are simplified teaching illustrations of inheritance, and the blood-type mode predicts only ABO/Rh blood type, not any disease risk.
Why does the three-gene mode let me skip the third gene?
Not every cross involves three genes — the option to mark the third gene “not used” lets the calculator behave as a standard two-gene (dihybrid) cross when only two genes are relevant, without forcing an artificial third-gene entry.
What’s the difference between genotype and phenotype in these results?
Genotype refers to the actual allele combination (like AA, Aa, or aa), while phenotype refers to the observable trait that results from that genotype (such as dominant or recessive appearance) — this calculator reports probabilities for both, since a given phenotype can result from more than one genotype.
