Generate Punnett squares for monohybrid and dihybrid crosses. See genotype and phenotype ratios with a visual grid and probability bars.
Last updated: March 2, 2026
Generate Punnett squares for monohybrid and dihybrid crosses. See genotype and phenotype ratios with a visual grid and probability bars. This tool runs in-browser for fast results without account setup.
Yes. This generator is completely free with no signup required. It runs entirely in your browser.
A Punnett square is a diagram that shows all possible genotype combinations from a genetic cross. It was named after geneticist Reginald Punnett.
An Aa × Aa cross produces a 1:2:1 genotype ratio (1 AA : 2 Aa : 1 aa) and a 3:1 phenotype ratio (3 dominant : 1 recessive).
An AaBb × AaBb cross produces Mendel's famous 9:3:3:1 phenotype ratio, assuming independent assortment of the two genes.
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Quick examples
| A | a | |
|---|---|---|
| A | AA | Aa |
| a | Aa | aa |
Genotype ratio: 1:2:1
Phenotype ratio: 3:1
A Punnett square is a diagram used to predict the genotype and phenotype outcomes of a genetic cross. Named after geneticist Reginald Punnett, it displays all possible combinations of parental gametes.
Monohybrid cross (1 gene): A 2×2 grid showing 4 possible offspring. The classic Aa × Aa cross produces a 1:2:1 genotype ratio and 3:1 phenotype ratio.
Dihybrid cross (2 genes): A 4×4 grid with 16 possible offspring. The classic AaBb × AaBb cross produces Mendel's famous 9:3:3:1 phenotype ratio, assuming independent assortment.
Uppercase letters represent dominant alleles, lowercase represent recessive alleles. In simple dominance, one copy of the dominant allele is sufficient to express the dominant phenotype.