What is the genotype ratio for Aa × Aa?

The expected genotype ratio is 1 AA : 2 Aa : 1 aa, or 25%, 50%, and 25%.

What is the phenotype ratio for Aa × Aa?

With complete dominance, Aa × Aa usually gives a 3:1 dominant-to-recessive phenotype ratio.

Can this calculator do dihybrid crosses?

No. This version focuses on one gene with two alleles. Dihybrid crosses require a larger Punnett square.

Is this the same as Hardy-Weinberg?

No. A Punnett square predicts offspring probabilities from parental allele contributions, while Hardy-Weinberg describes population genotype frequencies under specific assumptions.

Punnett Square Calculator

Estimate genotype probabilities for a simple two-allele Mendelian cross using parental dominant allele frequencies.

Parent 1 dominant allele frequencyParent 2 dominant allele frequency

Punnett Square Probability Formula

AA = p1×p2; Aa = p1(1-p2)+(1-p1)p2; aa=(1-p1)(1-p2)

This calculator models the probability that each parent contributes a dominant or recessive allele. It then combines those gamete probabilities to estimate AA, Aa, and aa offspring outcomes.

Symbol	Variable	Description
p1	Parent 1 dominant allele chance	Probability that parent 1 contributes the dominant allele.
p2	Parent 2 dominant allele chance	Probability that parent 2 contributes the dominant allele.
AA/Aa/aa	Genotypes	Possible offspring genotype classes for one gene with two alleles.

How to Use the Punnett Square Calculator

1
Enter parent allele probabilities
Use 50% when a heterozygous parent has an equal chance to pass the dominant or recessive allele.
2
Calculate genotype outcomes
The calculator returns AA, Aa, and aa probabilities for a simple monohybrid cross.
3
Interpret phenotype carefully
For a complete-dominance trait, AA and Aa usually show the dominant phenotype, while aa shows the recessive phenotype.

Common Monohybrid Cross Examples

For an Aa × Aa cross, each parent contributes A 50% of the time and a 50% of the time. The expected genotype ratio is 1 AA : 2 Aa : 1 aa, which means 25% AA, 50% Aa, and 25% aa.

Cross	Expected result
Aa × Aa	1:2:1 genotype ratio
AA × aa	100% Aa offspring
Aa × aa	50% Aa and 50% aa
Aa × Aa, complete dominance	3:1 phenotype ratio

What This Calculator Can and Cannot Model

This Punnett square calculator is designed for a single gene with two alleles. It is useful for introductory genetics, homework checks, and quick probability reasoning, but it does not model linkage, multiple genes, incomplete penetrance, sex linkage, or non-Mendelian inheritance.

Use it for simple dominant/recessive monohybrid crosses.
Do not use it as a full genetic counseling tool.
For population-level allele frequency questions, use an allele frequency or Hardy-Weinberg calculator instead.

Punnett Square FAQ

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