Punnett Square Calculator

Predict offspring genotype and phenotype ratios from two parents' alleles, for up to three genes.

Parent 1 genotype	AaBb
Parent 2 genotype	AaBb

Parent 1 genotype

One letter pair per gene: uppercase dominant, e.g. Aa or AaBb.

Parent 2 genotype

Phenotype ratio

9 : 3 : 3 : 1

A_ B_: 56.25%; A_ bb: 18.75%; aa B_: 18.75%; aa bb: 6.25% (_ = either allele).

Punnett square

	AB	Ab	aB	ab
AB	AABB	AABb	AaBB	AaBb
Ab	AABb	AAbb	AaBb	Aabb
aB	AaBB	AaBb	aaBB	aaBb
ab	AaBb	Aabb	aaBb	aabb

Genotypes

Genotype	Probability
AaBb	25%
AABb	12.5%
AaBB	12.5%
Aabb	12.5%
aaBb	12.5%
AABB	6.25%
AAbb	6.25%
aaBB	6.25%
aabb	6.25%

About the Punnett Square Calculator

Enter each parent's genotype, such as AaBb, with capitals for dominant alleles. The calculator lists every gamete combination and gives the genotype and phenotype ratios of the offspring.

Each parent passes on one allele of each gene at random. A Punnett square lists every combination of the parents' gametes. For independently assorting genes with complete dominance, a dihybrid cross of two AaBb parents gives the classic 9 : 3 : 3 : 1 phenotype ratio.

The formula

P(offspring genotype) = Σ P(gamete₁) × P(gamete₂)

Worked example

Two AaBb parents (a dihybrid cross)

Each makes four gametes: AB, Ab, aB, ab
16 combinations
Phenotypes 9 : 3 : 3 : 1 (56.25%, 18.75%, 18.75%, 6.25%)

Things to keep in mind

Assumes complete dominance and independent assortment (no linkage).

Questions people ask

What does Aa mean?

One dominant (A) and one recessive (a) allele: heterozygous.

Why 9:3:3:1?

Two independent 3:1 ratios multiplied together.