Dihybrid Cross Calculator
Analyze the genetic outcomes of crossing two traits. Enter the parental genotypes for Gene 1 (A/a) and Gene 2 (B/b) to generate the 4x4 Punnett square.
Parental Genotypes
Select the genotype for both parents for Gene 1 and Gene 2.
Parent 1 (Mother)
Parent 2 (Father)
4×4 Punnett Square
| AB | Ab | aB | ab | |
|---|---|---|---|---|
| AB | AABB | AABb | AaBB | AaBb |
| Ab | AABb | AAbb | AaBb | Aabb |
| aB | AaBB | AaBb | aaBB | aaBb |
| ab | AaBb | Aabb | aaBb | aabb |
Offspring Probabilities
Phenotypic Ratio (Simple Dominance)
Top Genotypes
Expert Tip
A classic Mendelian dihybrid cross between two double heterozygotes (AaBb × AaBb) will always yield a characteristic phenotypic ratio of 9:3:3:1.
Methodology & Equations
The Dihybrid Cross Principle
Gregor Mendel's Law of Independent Assortment states that alleles of two (or more) different genes get sorted into gametes independently of one another. For two heterozygous parents (AaBb), each parent produces four possible gametes with equal frequency: AB, Ab, aB, and ab.
Mendelian Phenotypes
Assuming complete dominance:
- f(A_B_) = Dominant for both traits (Expected: 9/16)
- f(A_bb) = Dominant for Gene 1, Recessive for Gene 2 (Expected: 3/16)
- f(aaB_) = Recessive for Gene 1, Dominant for Gene 2 (Expected: 3/16)
- f(aabb) = Recessive for both traits (Expected: 1/16)
How to Calculate a Dihybrid Cross: Step-by-Step
Below is a step-by-step walkthrough of crossing two double heterozygous parents (AaBb × AaBb):
Determine Parent Gametes
Find all unique combinations of Gene 1 and Gene 2 alleles for each parent. For genotype AaBb, the possible gametes are: AB, Ab, aB, and ab.
Set Up the 4x4 Grid
Place Parent 1 gametes along the top column headers, and Parent 2 gametes along the left row headers of a 4×4 table.
Combine Alleles in Each Cell
For each box in the grid, combine the corresponding row and column gametes. Rearrange the resulting letters so alleles of the same gene are grouped together, with capital letters first (e.g., crossing gamete Ab with aB results in genotype AaBb).
Related Calculators
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Punnett Square Calculator
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Trihybrid Cross
Analyze offspring genotype and phenotype probabilities for a three-gene cross.