Punnett Square Calculator
Use this Punnett square calculator to build monohybrid or dihybrid crosses, list the offspring genotypes, and summarize the simple dominant phenotype ratio.
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Run the calculator.
What This Punnett Square Calculator Helps You Do
This page creates the full Punnett square and then summarizes the result, which is faster than filling each cell by hand when checking classroom genetics examples.
It focuses on the standard monohybrid and dihybrid cases that most learners use when they want genotype and phenotype ratios from simple dominance.
How to Calculate Punnett Square Calculator
- Choose mono- or dihybrid mode: Monohybrid mode expects one allele pair per parent, while dihybrid mode expects two pairs.
- Enter valid genotypes: Use standard forms such as Aa or AaBb, keeping each gene pair together.
- Generate gametes: The calculator lists all possible gametes each parent can contribute.
- Count genotype and phenotype ratios: Each cell in the Punnett square contributes to the final distribution summary.
Punnett Square Calculator Formula
| Variable | Meaning | Unit |
|---|---|---|
| Parent genotype | Allele pairs contributed by each parent | letters |
| Gametes | Possible allele combinations in reproductive cells | letters |
| Genotype ratio | Count of each offspring genotype | count or percent |
| Phenotype ratio | Dominant or recessive trait outcome under simple dominance | count or percent |
Use the worked examples below to check how the formula behaves with real values. If the result looks unexpected, verify the unit assumptions and the meaning of each variable before interpreting the answer.
Worked Examples
- Parent 1: Aa
- Parent 2: Aa
Result: Genotypes are 1 AA : 2 Aa : 1 aa, with a 3:1 dominant-to-recessive phenotype ratio.
This is the classic introductory Punnett square example for simple dominance.
- Parent 1: AaBb
- Parent 2: AaBb
Result: The 16-cell square produces the classic 9:3:3:1 phenotype ratio under simple dominance.
Dihybrid mode assumes independent assortment and simple dominant-recessive inheritance for both genes.
How to Interpret Your Results
| Range | Meaning | Action |
|---|---|---|
| Monohybrid cross | The square has 4 cells. | Use this for one-gene inheritance examples. |
| Dihybrid cross | The square has 16 cells. | Use this when tracking two independent gene pairs. |
| Simple dominance phenotype summary | Any uppercase allele is treated as dominant. | More complex inheritance patterns require a different model. |
Frequently Asked Questions
References
Last reviewed: March 2026