What is a dihybrid cross?

A dihybrid cross involves two parents that differ in two independent traits (gene pairs). It produces a 4x4 Punnett square with 16 possible offspring genotype combinations.

Why does AaBb x AaBb give a 9:3:3:1 ratio?

With two independently assorting genes and complete dominance, 9 offspring have at least one dominant allele at both loci, 3 are dominant only at Gene 1, 3 are dominant only at Gene 2, and 1 is homozygous recessive at both loci.

What notation should I use?

Use one letter per allele. Uppercase (A, B) = dominant; lowercase (a, b) = recessive. The two genes must use different letters (e.g., A/a for Gene 1, B/b for Gene 2).

Does this assume independent assortment?

Yes. The tool assumes the two genes are on different chromosomes (or far apart on the same chromosome) so they assort independently, following Mendel's second law.

What if I want incomplete dominance or codominance?

This tool models complete dominance only. For incomplete dominance or codominance you would need to redefine phenotype classes manually based on the genotype output shown in the grid.

What is the difference between dihybrid and monohybrid?

A monohybrid cross tracks one gene and produces a 2x2 grid (4 cells). A dihybrid cross tracks two genes and produces a 4x4 grid (16 cells), capturing how two traits are inherited together.

Punnett Square Dihybrid

Name: Punnett Square Dihybrid
Availability: InStock
Author: Nham Vu

Enter two-gene parent genotypes (e.g. AaBb x AaBb) and instantly see the 4x4 Punnett square with all 16 offspring combinations, genotype counts, and phenotype ratios.

Parent Genotypes

Parent 1

Gene 1

Gene 2

Parent 2

Gene 1

Gene 2

Examples:

Punnett Square (4 x 4 = 16 combinations)

Top row = Parent 2 gametes | Left column = Parent 1 gametes

Genotype Counts (out of 16)

Phenotype Ratios (complete dominance assumed)

Enter parent alleles above to generate the dihybrid Punnett square.

Summary

Enter two-gene parent genotypes (e.g. AaBb x AaBb) and instantly see the 4x4 Punnett square with all 16 offspring combinations, genotype counts, and phenotype ratios.

How it works

Enter the two alleles for Gene 1 (e.g., A and a) and Gene 2 (e.g., B and b) for Parent 1.
Enter the same for Parent 2.
The tool generates all four gamete combinations for each parent (e.g., AB, Ab, aB, ab).
The 4x4 grid is filled by pairing each of Parent 1's four gametes with each of Parent 2's four gametes, giving 16 offspring cells.
Each cell shows the two-gene genotype (e.g., AaBb). Cells are color-coded by phenotype class.
Genotype counts and phenotype ratios are tallied and displayed as ratio bars below the grid.

Use cases

Predict offspring ratios for a two-trait cross in genetics homework or exams.
Verify the classic 9:3:3:1 phenotype ratio for AaBb x AaBb crosses.
Model independent assortment of two unlinked genes.
Explore how changing parent genotypes shifts the expected offspring ratios.
Assist plant and animal breeders in estimating multi-trait expression rates.
Demonstrate Mendel's Law of Independent Assortment in classroom settings.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu