Enter two parent genotypes such as AaBb to draw the Punnett square for up to four genes, with genotype and phenotype ratios as fractions and percentages.
Two heterozygous pea plants, AaBb and AaBb, give four kinds of gamete each, and the sixteen boxes between them hold the famous 9 : 3 : 3 : 1. Type both parents’ genotypes into this Punnett Square Calculator and it draws the grid, colours each box by phenotype, and counts the ratios for you.
It handles monohybrid through four-gene crosses. Any gene can be switched to incomplete dominance, where the heterozygote looks like a blend of the two parents. Fractions come out reduced, and each one also appears as a percentage.
The tool opens on AaBb × AaBb with both genes fully dominant. You see:
AB, Ab, aB, ab along both edges, making a 4 × 4 grid of 16 boxesClick a phenotype such as aa bb and every other box fades, so you can see the single corner cell it comes from. Load Sample steps on to a 3 : 1 monohybrid cross, a snapdragon Rr × Rr with R set to blend (1 : 2 : 1), a 64-box trihybrid and two test crosses.
Each parent’s gametes are every combination of one allele per gene, so n genes give 2n gametes. Duplicates are kept: AA still contributes two A columns, as it would on paper. Each box joins one gamete from each parent. A_ means at least one dominant allele, which covers AA and Aa.
Ratios are divided by their greatest common factor. Genes are assumed to assort independently, which holds for genes on different chromosomes. Linked genes, sex-linked traits and epistasis need a different model, and this tool does not attempt them.
Letter order and spacing are forgiven. aA becomes Aa, and Bb Aa is read as AaBb. A mismatched pair is caught with a specific message: “Parent 1: "Ab" is not an allele pair. Both letters of a gene must be the same letter, as in AA, Aa or aa.” Parents must carry the same genes.
The ceiling is 4 genes, a 16 × 16 grid of 256 boxes. A fifth gene would need 1,024 boxes, so it is refused with a note saying so. The arrow button between the two inputs swaps the parents, which moves each gamete set to the other edge of the grid without changing any ratio.
One letter per gene, capital for the dominant allele: Aa, AaBb, AaBbCc. Up to 4 genes; order and spacing don't matter.
Incomplete dominance (heterozygote shows a blend)
AaBb × AaBb · 4 × 4 = 16 boxes
9 : 3 : 3 : 1
phenotype ratio · genotype ratio 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1
| Parent 2 gametes down, parent 1 gametes across | AB | Ab | aB | ab |
|---|---|---|---|---|
| AB | AABB | AABb | AaBB | AaBb |
| Ab | AABb | AAbb | AaBb | Aabb |
| aB | AaBB | AaBb | aaBB | aaBb |
| ab | AaBb | Aabb | aaBb | aabb |
Parent 1's gametes run across the top, parent 2's down the side. Click any row below to highlight its boxes.
Phenotypes
| 9/16 | 56.25% | |
| 3/16 | 18.75% | |
| 3/16 | 18.75% | |
| 1/16 | 6.25% |
Genotypes
| 1/16 | 6.25% | |
| 1/8 | 12.50% | |
| 1/16 | 6.25% | |
| 1/8 | 12.50% | |
| 1/4 | 25% | |
| 1/8 | 12.50% | |
| 1/16 | 6.25% | |
| 1/8 | 12.50% | |
| 1/16 | 6.25% |
A_ means at least one dominant A allele (AA or Aa look the same). Genes are assumed to assort independently, as Mendel's second law states for unlinked genes.