Punnett Square Calculator
Build Punnett squares for monohybrid and dihybrid crosses (Aa × Aa, AaBb × AaBb) and get genotype and phenotype ratios and probabilities.
How to use
- 1Enter each parent's genotype with one letter pair per gene, e.g. Aa or AaBb.
- 2Uppercase letters are dominant alleles; use the same letters for both parents.
How it's calculated
Each parent's gametes combine every allele choice; all pairings are equally likely. Phenotypes assume complete dominance.
Frequently asked questions
What ratio does Aa × Aa give?
Genotypes 1 AA : 2 Aa : 1 aa, and phenotypes 3 dominant : 1 recessive.
What about AaBb × AaBb?
The classic 9 : 3 : 3 : 1 phenotype ratio, assuming the genes are on different chromosomes (independent assortment).
Does this handle incomplete dominance?
Genotype ratios are always correct; phenotype ratios assume complete dominance, so interpret them differently for incomplete or co-dominance.