Use our free Punnett Square Calculator to explore how genetic traits may be passed from parents to offspring. Calculate monohybrid and dihybrid crosses, view possible allele combinations, and find genotype and phenotype probabilities. Choose a P Cross, F1 × F1, or Test Cross preset to help with common genetics problems, or enter your own parent genotypes. It’s a simple, interactive way to learn the basics of Mendelian genetics.
Choose the type of genetic cross, select each parent’s genotype, and explore the possible offspring combinations and their expected probabilities.
Choose one gene or two genes at a time.
A preset fills in example genotypes you can change.
Choose genotypes above to view the Punnett square and genetic ratios.
How to Use the Punnett Square Calculator
- Choose the cross type: Select Monohybrid for one gene or Dihybrid for two genes.
- Select a cross preset: Choose P Cross, F1 × F1, or Test Cross to load a common genetics example.
- Choose the parent genotypes: You can keep the preset values or select different genotypes for both parents.
- View the Punnett square: Each cell shows a possible offspring genotype and the probability of that individual combination.
- Check the results: Review genotype probabilities, phenotype probabilities, and their expected ratios.
Example: Monohybrid Cross (Aa × Aa)
Suppose a plant has a dominant allele A for purple flowers and a recessive allele a for white flowers. Both parent plants have the genotype Aa.
The possible offspring combinations are:
| Offspring genotype | Probability |
|---|---|
| AA | 25% |
| Aa | 50% |
| aa | 25% |
The expected genotype ratio is 1 AA : 2 Aa : 1 aa.
Because A is dominant, both AA and Aa plants are expected to have purple flowers. Only aa plants are expected to have white flowers.
- Purple flowers: 75%
- White flowers: 25%
- Expected phenotype ratio: 3:1
These are theoretical probabilities, not a guarantee that every group of four offspring will contain exactly three purple-flowered plants and one white-flowered plant.
Example: Dihybrid Cross (AaBb × AaBb)
Suppose two plants are heterozygous for two genes. A represents a dominant trait for the first gene, and B represents a dominant trait for the second gene.
Under complete dominance and independent assortment, the expected phenotype ratio is 9:3:3:1:
- Both dominant traits (A_B_): 9/16 or 56.25%
- A dominant and B recessive (A_bb): 3/16 or 18.75%
- A recessive and B dominant (aaB_): 3/16 or 18.75%
- Both recessive traits (aabb): 1/16 or 6.25%
The calculator shows the possible allele combinations and their calculated probabilities.
What Do P Cross, F1 × F1, and Test Cross Mean?
- P Cross: A cross between parental-generation organisms. For example, AABB × aabb in a two-gene example.
- F1 × F1: A cross between two first-generation offspring. For example, AaBb × AaBb.
- Test Cross: A cross with a homozygous recessive organism to help investigate an unknown genotype. For example, Aa × aa for one gene.
These presets are starting examples. You can select different parent genotypes to explore other crosses.
Disclaimer: This calculator is designed for basic Mendelian genetics. Its phenotype predictions assume complete dominance. Dihybrid predictions also assume independent assortment of the two genes. Real inheritance can be more complex, including incomplete dominance, codominance, linkage, and other genetic effects. The results are theoretical probabilities for learning and educational use.