How do I enter the parents for a Punnett square?

Give each parent one to three two-letter allele pairs, such as Aa, AaBb or AaBbCc. Each pair must use the same Latin letter, and both parents must contain the same loci. Use case to distinguish the alleles and omit spaces between pairs. The tool normalizes aA to Aa and sorts loci by letter.

What does Aa crossed with Aa produce?

The exact genotype probabilities are AA 1/4, Aa 1/2 and aa 1/4, a 1:2:1 ratio. Under complete dominance, AA and Aa share a phenotype, giving 3:1. Incomplete dominance and codominance keep the heterozygote distinct, giving three display categories in a 1:2:1 ratio.

Can this generator make a dihybrid or trihybrid cross?

Yes. It supports up to three independent two-allele loci. AaBb crossed with aabb produces AaBb, Aabb, aaBb and aabb, each with probability 1/4. AaBbCc crossed with AaBbCc makes an 8 by 8 grid with 64 cells. Linked loci are outside this model.

Why is a homozygous cross a smaller grid?

Identical gametes are merged before the parents are crossed, retaining their integer allele-choice weights. AABB makes only AB gametes, with probability 1. AABB crossed with aabb therefore needs one cell and produces AaBb with probability 1. Each cell probability is the product of its row and column gamete probabilities.

Can I download a blank worksheet and an answer key?

Yes. Student SVG and Answer-key SVG are separate downloads. PDF worksheet + key creates a real PDF with separate student and answer-key pages on US Letter paper. The exports include gamete probabilities, combined weights, fictional labels and model assumptions. The PDF font supports basic Latin and common Western European characters; labels containing unsupported characters remain available in SVG.

Do edited trait labels change the probabilities?

No. Labels name fictional plant traits and phenotype categories. The allele pairs and selected dominance convention determine the outcomes. Custom names are shown as literal text in the grid's accompanying probability tables and worksheets. Reusing a name does not combine otherwise distinct phenotype categories.

Does a 3:1 ratio predict the counts in four offspring?

No. The ratio expresses probabilities under equal segregation and independent assortment. It does not require every group of four offspring to contain exactly three of one phenotype and one of the other. The tool is for symbolic teaching examples, not real-person traits, disease risk or reproductive predictions.

Are my inputs uploaded or saved?

The calculation and worksheet creation run in your browser without uploading the inputs. A draft is saved in this browser when you edit the form, if local storage is available. Default fictional labels are not saved unless you edit them. Restoring a draft does not generate a result; choose Generate cross to calculate it.

Punnett Square Lab

Explore symbolic Mendelian crosses with one to three independent two-allele loci. See weighted gametes, a grid of up to 64 cells, and exact genotype and phenotype ratios, then export an original worksheet and separate answer key. Choose a dominance display and optional fictional plant labels.

Symbolic parents1 independent locus

Gametes and offspringEqual segregation

Explore an exact cross

Start with Aa × Aa, or enter up to three independent loci. The grid appears after you generate.

Enter matching loci and choose Generate cross to see the outcomes.

Grid

Not generated

Genotypes

Pending

Probability sum

Pending

Phenotype ratio

Pending

SVG downloads keep the blank worksheet and answer key separate. PDF includes separate student and key pages on US Letter paper. Its built-in font supports basic Latin and common Western European characters; use SVG for other characters.

Worked examples

One locus

Aa × Aa: AA 1/4, Aa 1/2, aa 1/4. Complete-dominance phenotype ratio 3:1.

Test cross

AaBb × aabb: AaBb, Aabb, aaBb and aabb, each 1/4.

Fixed gametes

AABB × aabb: AB × ab gives AaBb with probability 1.

Common questions

How do I enter the parents for a Punnett square?: Give each parent one to three two-letter allele pairs, such as Aa, AaBb or AaBbCc. Each pair must use the same Latin letter, and both parents must contain the same loci. Use case to distinguish the alleles and omit spaces between pairs. The tool normalizes aA to Aa and sorts loci by letter.
What does Aa crossed with Aa produce?: The exact genotype probabilities are AA 1/4, Aa 1/2 and aa 1/4, a 1:2:1 ratio. Under complete dominance, AA and Aa share a phenotype, giving 3:1. Incomplete dominance and codominance keep the heterozygote distinct, giving three display categories in a 1:2:1 ratio.
Can this generator make a dihybrid or trihybrid cross?: Yes. It supports up to three independent two-allele loci. AaBb crossed with aabb produces AaBb, Aabb, aaBb and aabb, each with probability 1/4. AaBbCc crossed with AaBbCc makes an 8 by 8 grid with 64 cells. Linked loci are outside this model.
Why is a homozygous cross a smaller grid?: Identical gametes are merged before the parents are crossed, retaining their integer allele-choice weights. AABB makes only AB gametes, with probability 1. AABB crossed with aabb therefore needs one cell and produces AaBb with probability 1. Each cell probability is the product of its row and column gamete probabilities.
Can I download a blank worksheet and an answer key?: Yes. Student SVG and Answer-key SVG are separate downloads. PDF worksheet + key creates a real PDF with separate student and answer-key pages on US Letter paper. The exports include gamete probabilities, combined weights, fictional labels and model assumptions. The PDF font supports basic Latin and common Western European characters; labels containing unsupported characters remain available in SVG.
Do edited trait labels change the probabilities?: No. Labels name fictional plant traits and phenotype categories. The allele pairs and selected dominance convention determine the outcomes. Custom names are shown as literal text in the grid's accompanying probability tables and worksheets. Reusing a name does not combine otherwise distinct phenotype categories.
Does a 3:1 ratio predict the counts in four offspring?: No. The ratio expresses probabilities under equal segregation and independent assortment. It does not require every group of four offspring to contain exactly three of one phenotype and one of the other. The tool is for symbolic teaching examples, not real-person traits, disease risk or reproductive predictions.
Are my inputs uploaded or saved?: The calculation and worksheet creation run in your browser without uploading the inputs. A draft is saved in this browser when you edit the form, if local storage is available. Default fictional labels are not saved unless you edit them. Restoring a draft does not generate a result; choose Generate cross to calculate it.

Textbook independent assortment with equal allele segregation and chosen dominance convention only. No linked genes, penetrance, real-person traits, disease risks, fertility or reproductive advice. Ratios describe the model, not guaranteed counts in actual offspring.