Why does a dihybrid cross use a 4×4 Punnett square?

A dihybrid cross tracks two genes at once. Each parent can make up to four gamete combinations (AB, Ab, aB, ab), so the square is 4×4.

Can I use different allele letters like R/r?

Yes. Change the allele letters in Trait settings and the genotype dropdowns will update automatically.

All calculators

Punnett Square Calculator

Build Punnett squares for one or two traits (monohybrid / dihybrid), auto-generate gametes, and get genotype + phenotype ratios with a clean visual. Includes step-by-step and quick picks for common exam crosses.

Background

A Punnett square predicts the probability of offspring genotypes (and phenotypes) from two parents. The trick is always the same: list each parent’s gametes, fill the grid, then count outcomes.

Build your Punnett square

Number of traits

One trait (2×2)

Two traits (4×4)

Tip: Dihybrid squares get big fast—this calculator auto-builds gametes for you.

Trait settings

Trait 1 allele letters

Trait 1 phenotype labels (optional)

If you leave phenotype labels blank, we’ll show phenotypes as “Dominant present” vs “Recessive only.”

Parents

Parent 1 genotype

Example: Aa (heterozygous)

Parent 2 genotype

Example: AaBb (heterozygous for both)

Gametes: — Square: — Click a cell to highlight its phenotype

Options:

Show step-by-step

Show genotype + phenotype ratios

Show mini ratio bars

Quick picks:

Prefills parents and runs the calculator.

Result:

No results yet. Choose parents and click Calculate.

How to use this calculator

Pick one or two traits.
Set allele letters (defaults: A/a and B/b) and optional phenotype labels.
Select each parent’s genotype from the dropdowns.
Click Calculate to generate the square and ratios.
Click any cell to highlight that genotype/phenotype and see its probability.

How this calculator works

Gametes: each parent forms gametes containing one allele per gene.
Grid: rows are Parent 1 gametes; columns are Parent 2 gametes.
Fill: each cell combines the alleles from one row + one column.
Count: tally genotypes and phenotypes to get ratios and %.

Formula & Equation Used

Probability: P = (count / total) × 100%

Phenotype rule: dominant phenotype occurs if at least one dominant allele is present.

Examples

Example 1 — Monohybrid: Aa × Aa

Each parent makes gametes A and a. Fill the 2×2 square and count: genotypes AA : Aa : aa = 1 : 2 : 1, phenotypes Dominant : Recessive = 3 : 1.

Example 2 — Test cross: Aa × aa

Gametes: Aa → A, a and aa → a. Outcomes: Aa and aa in a 1 : 1 ratio. That means 50% dominant phenotype and 50% recessive phenotype.

Example 3 — Dihybrid: AaBb × AaBb

Each parent can make four gametes: AB, Ab, aB, ab. The 4×4 square has 16 outcomes. With independent assortment, the classic phenotype ratio is 9 : 3 : 3 : 1.