Punnett Square Calculator
Model single-gene inheritance. Enter the alleles for both parents to generate an intetive 2x2 Punnett square grid and calculate offspring genotype and phenotype probabilities.
Parental Genotypes
Input Parent 1 and Parent 2 alleles (uppercase = dominant, lowercase = recessive).
2×2 Punnett Grid
| A | a | |
|---|---|---|
| A | AA | Aa |
| a | Aa | aa |
Offspring Genotypes & Phenotypes
Genotype Ratio
Phenotype Ratio (Simple Dominance)
Genetics Formatting Convention
Always write the dominant (uppercase) allele first in heterozygous combinations (e.g. write "Aa" instead of "aA") for consistent genetic notation.
Classic Mendelian Monohybrid Cross Reference Table
| Parental Cross | Genotypic Ratio | Dominant Phenotype % | Recessive Phenotype % |
|---|---|---|---|
| AA × AA (Homozygous Dom × Dom) | 100% AA | 100% | 0% |
| AA × aa (Test Cross) | 100% Aa | 100% | 0% |
| Aa × Aa (Heterozygous Cross) | 1 AA : 2 Aa : 1 aa | 75% | 25% |
| Aa × aa (Backcross) | 1 Aa : 1 aa | 50% | 50% |
| aa × aa (Homozygous Rec × Rec) | 100% aa | 0% | 100% |
Calculation Methodology & Biological Principles
Mendel's Law of Segregation
Mendel's First Law states that allele pairs separate during gamete formation (meiosis), so each sperm or egg cell carries only one allele for each gene locus.
Key Genetics Terminology
Genotype: The exact genetic makeup (allele combination) of an organism.
Phenotype: The observable physical trait resulting from the genotype inteting with the environment.
Frequently Asked Questions
What is a Punnett Square? ▼
A Punnett square is a visual grid diagram invented by geneticist Reginald Punnett to determine the statistical probability of an offspring inheriting specific genotypes and phenotypes from two parents.
How do you determine dominant vs recessive alleles? ▼
Dominant alleles are represented by uppercase letters (e.g., 'A') and mask the expression of recessive alleles, which are represented by lowercase letters (e.g., 'a'). A dominant phenotype is expressed if at least one dominant allele is present.
What is the phenotypic ratio of a classic heterozygous monohybrid cross? ▼
Crossing two heterozygous parents (Aa × Aa) yields a classic Mendelian 3:1 phenotypic ratio (75% dominant phenotype, 25% recessive phenotype) and a 1:2:1 genotypic ratio (25% AA, 50% Aa, 25% aa).
Related Calculators
View All Biology Tools →Monohybrid Cross Calculator
Predict genotypic and phenotypic ratios of offspring for a single gene.
Dihybrid Cross Calculator
Generate a 4x4 Punnett square for a two-trait dihybrid cross.
Codominance Calculator
Analyze offspring ratios for co-expressed genetic traits.