Punnett Square Calculator
- Khan Academy — Mendelian genetics & Punnett squares
- Wikipedia — Punnett square (overview & history)
Use this Punnett Square Calculator to predict the possible genotypes and phenotypes of offspring for a simple one-gene cross. Select the genotype of each parent to view the expected probabilities for AA, Aa, and aa.
How a Punnett Square Works
Each parent contributes one allele to the offspring. The calculator combines the possible alleles from both parents in a 2 × 2 Punnett square.
- AA: homozygous dominant
- Aa: heterozygous
- aa: homozygous recessive
Under complete dominance, both AA and Aa show the dominant phenotype, while aa shows the recessive phenotype.
Worked Example
For the cross Aa × Aa, each parent can pass either A or a.
The possible offspring genotypes are:
- AA: 25%
- Aa: 50%
- aa: 25%
The expected genotype ratio is 1 AA : 2 Aa : 1 aa.
With complete dominance, the phenotype probabilities are:
- Dominant phenotype: 75%
- Recessive phenotype: 25%
Important Limitations
The results are probabilities, not guarantees for individual offspring. This calculator assumes one gene, two alleles, and complete dominance.
It does not model codominance, incomplete dominance, sex-linked inheritance, multiple alleles, linked genes, polygenic traits, mutations, or other complex inheritance patterns. It should not be used for medical genetic risk assessment or DNA-test interpretation.