Punnett Square Calculator
Model single-gene inheritance. Enter the alleles for both parents to generate a 2x2 Punnett square grid and calculate the genotypic and phenotypic ratios of the offspring.
Parental Genotypes
Input Parent 1 and Parent 2 alleles (use uppercase for dominant, lowercase for recessive).
2×2 Grid
| A | a | |
|---|---|---|
| A | AA | Aa |
| a | Aa | aa |
Offspring Genotypes & Phenotypes
Genotype Ratio
Phenotype Ratio (Simple Dominance)
Expert Tip
By convention, write the dominant (uppercase) allele first in heterozygous combinations (e.g., write "Aa", not "aA"). This makes reading the ratios much easier.
Methodology & Equations
The Punnett Square Concept
Invented by Reginald Punnett, the square is a tabular diagram used to predict the genotypes of a particular cross or breeding experiment.
Mendelian Terms
- Homozygous Dominant (AA): Carries two copies of the dominant allele. Shows dominant phenotype.
- Heterozygous (Aa): Carries one dominant and one recessive allele. Shows dominant phenotype.
- Homozygous Recessive (aa): Carries two copies of the recessive allele. Shows recessive phenotype.
How to Use a Punnett Square: Step-by-Step
Below is a step-by-step example crossing two heterozygous parents (Aa × Aa):
List Parental Gametes
Identify the alleles each parent can pass on. For genotype Aa, the gametes can be 'A' or 'a'.
Set Up the 2x2 Grid
Place Parent 1 alleles (A and a) as columns along the top, and Parent 2 alleles (A and a) as rows along the left side.
Cross the Alleles
Fill in each cell by combining the allele from the top column and left row. The resulting cells yield: AA (1/4), Aa (2/4), and aa (1/4).
Related Calculators
View All Biology Tools →Monohybrid Cross
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Dihybrid Cross Calculator
Generate a 4x4 Punnett square for a two-trait dihybrid cross.
Codominance Calculator
Analyze offspring ratios for co-expressed genetic traits.