Nuumia Editorial Team·Based on Mendel's Laws & NHGRI Genomics Glossary·Updated March 2026

Punnett Square Calculator — Monohybrid & Dihybrid Cross

Generate Punnett squares instantly for monohybrid (1 gene) and dihybrid (2 genes) crosses. View color-coded genotype and phenotype ratios.

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Quick Cross Example

Aa × Aa→1 AA : 2 Aa : 1 aa(3:1 phenotype ratio)

AaBb × AaBb→9:3:3:1(dihybrid phenotype ratio)

Punnett Square Calculator — Monohybrid & Dihybrid Crosses

The Punnett square is a grid diagram used to predict the probability of each genotype in offspring produced by two parents. This calculator supports monohybrid crosses (one gene, 2×2 grid, 4 outcomes) and dihybrid crosses (two independent genes, 4×4 grid, 16 outcomes), following Mendel's laws of segregation and independent assortment.

How the Punnett Square Works

List the gametes produced by each parent along the top row and left column. Each interior cell is filled with the allele combination from the corresponding column (Parent 1) and row (Parent 2). By convention the dominant allele (uppercase) is written before the recessive allele (lowercase). Counting each unique genotype gives the genotypic ratio; grouping cells by observable phenotype gives the phenotypic ratio.

Genotype & Phenotype Reference Table

Cross	Genotype Ratio	Phenotype Ratio	Type
Aa × Aa	1 AA : 2 Aa : 1 aa	3 dom : 1 rec	Monohybrid
AA × aa	all Aa	all dominant	Monohybrid
AA × Aa	1 AA : 1 Aa	all dominant	Monohybrid
Aa × aa	1 Aa : 1 aa	1 dom : 1 rec	Monohybrid
AA × AA	all AA	all dominant	Monohybrid
aa × aa	all aa	all recessive	Monohybrid
AaBb × AaBb	9 A_B_ : 3 A_bb : 3 aaB_ : 1 aabb	9:3:3:1	Dihybrid
AABB × aabb	all AaBb	all dom. A+B	Dihybrid P
AaBb × aabb	1:1:1:1	1:1:1:1	Testcross

FAQ — Punnett Square

A Punnett square is a diagram that organizes the possible gamete combinations of two parents to predict the expected genotype and phenotype ratios of their offspring.

A monohybrid cross tracks one gene and produces a 2×2 grid with 4 possible offspring combinations. A dihybrid cross tracks two independently assorting genes and produces a 4×4 grid with 16 combinations.

The cross Aa × Aa yields a 1:2:1 genotype ratio (1 AA : 2 Aa : 1 aa) and a 3:1 phenotype ratio (3 dominant : 1 recessive).

The 9:3:3:1 ratio is the classic phenotypic outcome of a dihybrid cross AaBb × AaBb. Out of 16 offspring: 9 show both dominant traits, 3 show dominant A only, 3 show dominant B only, and 1 shows both recessive traits.

Homozygous means both alleles of a gene are the same (AA or aa). Heterozygous means the two alleles differ (Aa). A heterozygous individual for two genes is called a dihybrid (e.g. AaBb).

Mendel's second law states that alleles for different genes distribute to gametes independently of one another, provided the genes are on different chromosomes (unlinked). This is the biological basis of the dihybrid Punnett square.

For a monohybrid cross enter exactly 2 characters representing the two alleles of one gene (e.g. Aa, AA, aa). For a dihybrid cross enter exactly 4 characters for two genes written consecutively (e.g. AaBb, AABB, aabb). Uppercase = dominant, lowercase = recessive.

Because AABB can only produce AB gametes, and aabb can only produce ab gametes. Every offspring therefore receives one A from Parent 1, one a from Parent 2, one B from Parent 1, and one b from Parent 2, giving 100% AaBb — the classic F1 result of a P-generation cross.

Sources & References

[1]Mendel, G.J. — Versuche über Pflanzenhybriden (Experiments on Plant Hybridization). Verhandlungen des naturforschenden Vereines in Brünn, 1866.↗
[2]National Human Genome Research Institute (NHGRI) — Punnett Square. NHGRI Talking Glossary of Genomic and Genetic Terms, 2023.↗
[3]LibreTexts Biology — Mendel's Law of Independent Assortment. Boundless General Biology, 2021.↗

This tool is for educational purposes only.

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	A	a
A	AA	Aa
a	Aa	aa

Genotype	Type	Phenotype
AA	Homozygous dominant	Dominant
Aa	Heterozygous	Dominant
aa	Homozygous recessive	Recessive
AABB	Double homozygous dom.	Dom. A + Dom. B
AaBb	Double heterozygous	Dom. A + Dom. B
aabb	Double homozygous rec.	Rec. A + Rec. B

Genotype

Type

Homozygous dominant

Heterozygous

Homozygous recessive

AABB

Double homozygous dom.

AaBb

Double heterozygous

aabb

Double homozygous rec.

Genotype	Type	Phenotype
AA	Homozygous dominant	Dominant
Aa	Heterozygous	Dominant
aa	Homozygous recessive	Recessive
AABB	Double homozygous dom.	Dom. A + Dom. B
AaBb	Double heterozygous	Dom. A + Dom. B
aabb	Double homozygous rec.	Rec. A + Rec. B

Genotype

Type

Homozygous dominant

Heterozygous

Homozygous recessive

AABB

Double homozygous dom.

AaBb

Double heterozygous

aabb

Double homozygous rec.

Punnett Square Calculator — Monohybrid & Dihybrid Crosses

How the Punnett Square Works

Genotype & Phenotype Reference Table

Cross	Genotype Ratio	Phenotype Ratio	Type
Aa × Aa	1 AA : 2 Aa : 1 aa	3 dom : 1 rec	Monohybrid
AA × aa	all Aa	all dominant	Monohybrid
AA × Aa	1 AA : 1 Aa	all dominant	Monohybrid
Aa × aa	1 Aa : 1 aa	1 dom : 1 rec	Monohybrid
AA × AA	all AA	all dominant	Monohybrid
aa × aa	all aa	all recessive	Monohybrid
AaBb × AaBb	9 A_B_ : 3 A_bb : 3 aaB_ : 1 aabb	9:3:3:1	Dihybrid
AABB × aabb	all AaBb	all dom. A+B	Dihybrid P
AaBb × aabb	1:1:1:1	1:1:1:1	Testcross

FAQ — Punnett Square

A Punnett square is a diagram that organizes the possible gamete combinations of two parents to predict the expected genotype and phenotype ratios of their offspring.

The cross Aa × Aa yields a 1:2:1 genotype ratio (1 AA : 2 Aa : 1 aa) and a 3:1 phenotype ratio (3 dominant : 1 recessive).

Homozygous means both alleles of a gene are the same (AA or aa). Heterozygous means the two alleles differ (Aa). A heterozygous individual for two genes is called a dihybrid (e.g. AaBb).

Sources & References

[1]Mendel, G.J. — Versuche über Pflanzenhybriden (Experiments on Plant Hybridization). Verhandlungen des naturforschenden Vereines in Brünn, 1866.↗
[2]National Human Genome Research Institute (NHGRI) — Punnett Square. NHGRI Talking Glossary of Genomic and Genetic Terms, 2023.↗
[3]LibreTexts Biology — Mendel's Law of Independent Assortment. Boundless General Biology, 2021.↗

Punnett Square Calculator — Monohybrid & Dihybrid Cross

Quick Cross Example

Punnett Square Calculator — Monohybrid & Dihybrid Crosses

How the Punnett Square Works

Genotype & Phenotype Reference Table

FAQ — Punnett Square

Sources & References

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Punnett Square Calculator — Monohybrid & Dihybrid Crosses

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Genotype & Phenotype Reference Table

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Sources & References

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Punnett Square Calculator — Monohybrid & Dihybrid Cross

Quick Cross Example

Punnett Square Calculator — Monohybrid & Dihybrid Crosses

How the Punnett Square Works

Genotype & Phenotype Reference Table

FAQ — Punnett Square

What is a Punnett square?

What is the difference between a monohybrid and a dihybrid cross?

What is the expected ratio for Aa × Aa?

What is the 9:3:3:1 ratio?

What does homozygous and heterozygous mean?

What is Mendel's law of independent assortment?

How do I enter genotypes in this calculator?

Why does AABB × aabb give all AaBb offspring?

Sources & References

Recommended Tools

BMI Calculator →

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Punnett Square Calculator — Monohybrid & Dihybrid Cross

Quick Cross Example

Punnett Square

Quick Presets

Genotype Reference

Genotype Reference

Punnett Square Calculator — Monohybrid & Dihybrid Crosses

How the Punnett Square Works

Genotype & Phenotype Reference Table

FAQ — Punnett Square

What is a Punnett square?

What is the difference between a monohybrid and a dihybrid cross?

What is the expected ratio for Aa × Aa?

What is the 9:3:3:1 ratio?

What does homozygous and heterozygous mean?

What is Mendel's law of independent assortment?

How do I enter genotypes in this calculator?

Why does AABB × aabb give all AaBb offspring?

Sources & References

Recommended Tools

BMI Calculator →

Meters to Inches →

Punnett Square

Quick Presets

Genotype Reference

Genotype Reference