Math July 13, 2026 · 8 Min Read

Dihybrid Cross Calculator – Guide & Formulas

Generate a 4x4 Punnett square for dihybrid crosses. Calculate phenotypic and genotypic ratios from parental genotypes for two independent Mendelian traits.

Generate a 4x4 Punnett square for dihybrid crosses and calculate phenotypic and genotypic ratios for two independent Mendelian traits.

Key Takeaway

Use the free Dihybrid Cross Calculator to generate a 4x4 punnett square for dihybrid crosses. calculate phenotypic and genotypic ratios from parental genotypes for two independent mendelian traits. Get instant results with step-by-step explanations.

How to Use the Dihybrid Cross Calculator

  1. Enter the genotype for Parent 1 (e.g., AaBb) using two gene symbols separated by no space.
  2. Enter the genotype for Parent 2 (e.g., AaBb) in the same format.
  3. Review the 4x4 Punnett square showing all 16 offspring genotype combinations.
  4. Check the phenotypic ratio — typically 9:3:3:1 for a heterozygous cross.
  5. Review the genotypic breakdown showing all unique genotypes and their frequencies.
  6. Use the results to predict offspring trait combinations in Mendelian crosses.

The Formula

A dihybrid cross combines two independently assorting genes. Each parent produces 4 gamete types. The Punnett square is a 4x4 grid (16 cells). For AaBb x AaBb: phenotypic ratio = 9:3:3:1 (dominant both : dominant A only : dominant B only : recessive both). Genotypic ratio has 9 distinct classes.

Variable Definitions

  • A, a: Two alleles of the first gene (A = dominant, a = recessive)
  • B, b: Two alleles of the second gene (B = dominant, b = recessive)
  • 9:3:3:1: Expected phenotypic ratio for AaBb x AaBb cross (two dominant : one dominant A only : one dominant B only : two recessive)
  • Gametes: Haploid cells carrying one allele from each gene — each parent produces 4 types
  • Independent assortment: Mendel's second law: alleles of different genes segregate independently during meiosis

Classic AaBb x AaBb Dihybrid Cross

Cross two parents both heterozygous for two genes: AaBb x AaBb. Gene A controls seed shape (R = round, r = wrinkled), Gene B controls seed color (Y = yellow, y = green).

  1. Step 1: Identify gametes. Parent 1 (AaBb) produces: AB, Ab, aB, ab. Parent 2 (AaBb) produces: AB, Ab, aB, ab.
  2. Step 2: Fill the 4x4 Punnett square. Each of 16 cells gets one gamete from each parent (4 rows x 4 columns).
  3. Step 3: Count phenotypes. Dominant A, Dominant B: 9/16. Dominant A, recessive b: 3/16. Recessive a, Dominant B: 3/16. Recessive a, recessive b: 1/16.
  4. Step 4: Phenotypic ratio = 9:3:3:1. For seed traits: 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green.
  5. Step 5: Genotypes: 9 unique genotypes with frequencies A_B_ = 9/16, A_bb = 3/16, aaB_ = 3/16, aabb = 1/16.

Frequently Asked Questions

What is a dihybrid cross?

A dihybrid cross tracks the inheritance of two genes simultaneously. Two parents heterozygous for both genes (e.g., AaBb x AaBb) produce a 4x4 Punnett square with 16 possible offspring genotype combinations.

What does the 9:3:3:1 ratio mean?

In a cross of two double heterozygotes (AaBb x AaBb) with independent assortment, the expected phenotypic ratio is 9:3:3:1. This means 9/16 show both dominant traits, 3/16 show one dominant trait, 3/16 show the other dominant trait, and 1/16 show both recessive traits.

Why is the Punnett square 4x4 instead of 2x2?

A monohybrid cross (one gene) produces a 2x2 square because each parent has 2 gamete types. A dihybrid cross (two genes) produces 4 gamete types per parent, resulting in a 4x4 square with 16 cells.

How do I determine gametes from a genotype?

For AaBb, use the FOIL method: First (AB), Outer (Ab), Inner (aB), Last (ab). Each gamete gets one allele from each gene — this gives 4 unique gamete combinations.

What if the genes are linked?

Linked genes on the same chromosome do not assort independently. The phenotypic ratio will deviate from 9:3:3:1. You need to know the recombination frequency to predict offspring. This calculator assumes independent assortment.

Can I use this for incomplete dominance or codominance?

Yes, but the phenotypic interpretation changes. In incomplete dominance, heterozygotes show an intermediate phenotype. The genotype ratios remain the same, but phenotypic ratios may be 1:2:1 for each gene instead of 3:1.

How do I calculate genotypic ratios from the Punnett square?

Count each unique genotype in the 16 cells. For AaBb x AaBb: AABB=1, AABb=2, AaBB=2, AaBb=4, AAbb=1, Aabb=2, aaBB=1, aaBb=2, aabb=1. Express as fractions of 16.

What is the difference between phenotypic and genotypic ratio?

Phenotypic ratio counts distinct physical appearances (e.g., round yellow vs. wrinkled green). Genotypic ratio counts distinct genetic compositions (e.g., AABB, AABb, AaBB are different genotypes that may share the same phenotype).

Can I cross parents with different genotypes?

Yes. For example, AaBb x Aabb produces different gamete sets and a different Punnett square. The calculator handles any valid two-gene genotype combination for both parents.

What if one parent is homozygous for one gene?

If Parent 1 is AABB and Parent 2 is aabb, all F1 offspring are AaBb. If crossing F1 (AaBb x AaBb), you get the classic 9:3:3:1 ratio. Different parent genotypes yield different gamete combinations and ratios.