Dihybrid Cross Calculator
The 16-square Punnett outcome of a cross between two parents for two independently assorting genes — the phenotype ratio, the genotype breakdown and the chance of a double recessive.
Each parent makes four kinds of gamete (one allele of each gene, all combinations); pairing every gamete of one parent with every gamete of the other gives sixteen equally likely offspring.
How the dihybrid cross calculator works
Each parent makes four kinds of gamete (one allele of each gene, all combinations); pairing every gamete of one parent with every gamete of the other gives sixteen equally likely offspring. Group them by phenotype — a capital allele is dominant — to get the ratio, 9:3:3:1 for two heterozygotes. Enter genotypes as four letters, the first pair for gene A and the second for gene B.
Formula: 16 combinations of 4 × 4 gametes; phenotype = dominant if any capital allele for that gene
Worked examples
| Inputs | Phenotype ratio | Note |
|---|---|---|
| AaBb × AaBb | 9:3:3:1 | 9:3:3:1 |
| Test cross AaBb × aabb | 1:1:1:1 | 1:1:1:1 |
| AABb × AaBb | 3:1 | 3:1 (all show A) |
FAQFrequently asked questions
Why 9:3:3:1?
Each gene in a heterozygote cross gives 3 dominant : 1 recessive; two independent genes multiply — 3×3 : 3×1 : 1×3 : 1×1. Any departure from it in real data means the genes are linked, or one allele is not fully dominant.
What is a test cross?
Crossing with a double recessive (aabb): the offspring phenotypes then reveal the other parent’s gametes directly, 1:1:1:1 for a heterozygote. Enter aabb as the second parent to see it.
Does this assume independent assortment?
Yes — the genes are on different chromosomes or far apart. Linked genes give fewer recombinant offspring than the square predicts; the recombination frequency measures how far apart they are.
Can I do three genes?
A trihybrid cross has 64 squares and a 27:9:9:9:3:3:3:1 ratio; the same logic applies but this calculator handles two. Multiply the single-gene probabilities for a specific outcome instead.
Where these figures come from
- NCBI Bookshelf — Molecular Biology of the Cell — growth kinetics and molecular conventions
- National Human Genome Research Institute — the US genomics research institute
Last checked: September 2026. Formulas are the standard textbook forms; assumptions are stated on each page because they are where these models break.