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Dihybrid Cross Calculator

Biology

Build a 16-square dihybrid cross for two genes (AaBb x AaBb) and get the classic 9:3:3:1 phenotype ratio with a full genotype breakdown instantly.

AB
Ab
aB
ab
AB
AABB
AABb
AaBB
AaBb
Ab
AABb
AAbb
AaBb
Aabb
aB
AaBB
AaBb
aaBB
aaBb
ab
AaBb
Aabb
aaBb
aabb
Dom / Dom
Dom / Rec
Rec / Dom
Rec / Rec

Phenotype Ratio

9 : 3 : 3 : 1
Dom / Dom
56.25%
Dom / Rec
18.75%
Rec / Dom
18.75%
Rec / Rec
6.25%

What is a Dihybrid Cross?

The Dihybrid Cross Calculator builds a full 16-square cross grid for two genes inherited independently, based on each parent's genotype for both genes. Select each parent's genotype (AA/Aa/aa for gene A, BB/Bb/bb for gene B), and the calculator instantly generates all 16 offspring genotype combinations along with the resulting phenotype ratio.

For the classic AaBb × AaBb cross, this produces the famous 9:3:3:1 ratio first described by Gregor Mendel. For single-gene crosses, see the Punnett Square Calculator.

How to use this Dihybrid Cross calculator

  1. Select Parent 1's genotype for Gene A and Gene B — choose AA, Aa, or aa for gene A, and BB, Bb, or bb for gene B.

  2. Select Parent 2's genotype for Gene A and Gene B — same options, independently for the second parent.

  3. Read the 16-square grid — each cell shows the combined genotype (e.g., AaBb) for that offspring combination, color-coded by phenotype category.

  4. Check the phenotype ratio — the highlighted result shows the reduced ratio (e.g., 9:3:3:1) along with the percentage breakdown for each of the four phenotype categories.

Formula & Methodology

Dihybrid cross process:
1. Each parent's genotype for gene A and gene B produces 4 gametes (every combination of one allele from each gene)
2. Crossing parent 1's 4 gametes against parent 2's 4 gametes produces 16 equally likely offspring combinations
3. Each offspring's genotype for gene A and gene B is normalized (dominant allele listed first)
4. Each offspring is classified as dominant or recessive for each gene, then grouped into one of 4 phenotype categories
5. Category counts are reduced to their simplest integer ratio using the greatest common divisor

Classic worked example (AaBb × AaBb):

Parent 1 gametes: AB, Ab, aB, ab

Parent 2 gametes: AB, Ab, aB, ab

Resulting 16-cell grid produces: 9 dominant/dominant, 3 dominant/recessive, 3 recessive/dominant, 1 recessive/recessive

Ratio: 9 : 3 : 3 : 1

Note: This model assumes the two genes assort independently (different chromosomes, or far apart on the same chromosome) and that dominance is complete for both genes. Linked genes, incomplete dominance, or codominance would require a different calculation.

Frequently Asked Questions

A dihybrid cross tracks the inheritance of two different genes simultaneously, typically illustrated with two heterozygous parents (AaBb × AaBb), producing the classic 9:3:3:1 phenotype ratio among 16 possible offspring combinations.
When both parents are heterozygous for two independently assorting genes (AaBb × AaBb), each parent produces 4 equally likely gamete types (AB, Ab, aB, ab), giving 16 equally likely offspring combinations in the cross grid — 9 show both dominant traits, 3 show the first dominant/second recessive, 3 show the first recessive/second dominant, and 1 shows both recessive traits.
Independent assortment (one of Mendel's laws) means the alleles for one gene segregate into gametes independently of the alleles for another gene, which is true when the two genes are on different chromosomes (or far apart on the same chromosome). This calculator assumes independent assortment, as does the standard 9:3:3:1 model.
Each parent's genotype for both genes produces 4 possible gametes (one allele from each gene, in every combination), and crossing 4 parent-1 gametes against 4 parent-2 gametes in a grid produces 16 total offspring combinations, each equally likely.
If a parent is homozygous for a gene (like AA or bb), it produces the same allele for that gene in every gamete, which changes the resulting ratio — this calculator supports any combination of AA/Aa/aa and BB/Bb/bb for both parents and calculates the correct resulting ratio automatically, not just the classic 9:3:3:1 case.
Genotype is the specific allele combination (like AaBb), shown in each grid cell, while phenotype is the observable trait outcome — whether each gene shows its dominant or recessive trait. The four phenotype categories (dominant/dominant, dominant/recessive, recessive/dominant, recessive/recessive) group multiple genotypes that look the same.
No — this calculator assumes independent assortment, which requires the two genes to be on different chromosomes or far enough apart on the same chromosome to recombine freely. Linked genes (close together on the same chromosome) don't follow the 9:3:3:1 pattern and require a different, linkage-based calculation.
A monohybrid cross tracks inheritance of a single gene (producing a 3:1 ratio for a heterozygous × heterozygous cross), while a dihybrid cross tracks two genes simultaneously (producing the 9:3:3:1 ratio). Try the [Punnett Square Calculator](/punnett-square-calculator/) for the simpler single-gene case.
This specific cross produces the maximally informative 9:3:3:1 ratio with all four phenotype combinations represented, making it the clearest illustration of independent assortment — Gregor Mendel's original pea plant experiments used exactly this kind of two-trait cross to establish the law.
No — 9:3:3:1 is the expected theoretical ratio based on probability across a very large number of offspring. Any individual real litter or brood can deviate from this ratio due to chance, especially with small sample sizes, similar to how flipping a fair coin 4 times won't always give exactly 2 heads and 2 tails.
A dihybrid cross predicts offspring ratios for one specific mating pair, while the [Allele Frequency Calculator](/allele-frequency-calculator/) and [Hardy-Weinberg Calculator](/hardy-weinberg-calculator/) describe allele and genotype distributions across an entire population — different scales of genetic analysis.
Also known as
9:3:3:1 calculatortwo gene cross calculatorAaBb x AaBb calculatordihybrid punnett square