Punnett Square Calculator (Monohybrid and Dihybrid)
Pick each parent’s genotype to see the chances of each offspring genotype and phenotype.
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Punnett Square Calculator (Monohybrid and Dihybrid) by TheCalcTools
How the Punnett Square Calculator (Monohybrid and Dihybrid) works
Each parent passes one of its two alleles to each child, each with a 50% chance. A Punnett square lists every combination; this calculator multiplies the same probabilities directly.
For two genes on different chromosomes (independent assortment), the chance of a combined phenotype is the product of the chances for each gene. Aa × Aa gives the classic 3:1 phenotype ratio, and AaBb × AaBb gives 9:3:3:1.
The formula
Worked example
Using the default values shown in the calculator:
| Parent 1, gene A | Aa (heterozygous) |
|---|---|
| Parent 2, gene A | Aa (heterozygous) |
| Second gene | No (monohybrid cross) |
| Parent 1, gene B | Bb (heterozygous) |
| Parent 2, gene B | Bb (heterozygous) |
- Aa × Aa: AA 25%, Aa 50%, aa 25% (1 : 2 : 1).
- So 75% show the dominant trait: a 3:1 ratio.
Result:
| Dominant phenotype for A | 75.00% |
|---|---|
| Recessive phenotype for A (aa) | 25.00% |
| AA | 25.00% |
| Aa | 50.00% |
| aa | 25.00% |
| Genotype ratio AA : Aa : aa | 1 : 2 : 1 |
| Dihybrid: both dominant traits (A_B_) | — |
| Dihybrid: dominant A, recessive b (A_bb) | — |
| Dihybrid: recessive a, dominant B (aaB_) | — |
| Dihybrid: both recessive (aabb) | — |
Frequently asked questions
Do real traits follow these ratios?
Only single-gene traits with complete dominance, such as the classic pea traits. Many human traits depend on many genes and the environment.
What if the genes are linked?
Genes close together on the same chromosome are inherited together more often than independent assortment predicts, so dihybrid ratios change.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.