What is Punnett Square?
The Punnett Square Calculator predicts the genotype and phenotype ratios of offspring from a genetic cross between two parents. Named after British geneticist Reginald Punnett, this tool is fundamental to Mendelian genetics and is taught in every biology class worldwide.
A Punnett Square is a grid that shows all possible combinations of alleles that offspring can inherit from their parents. For a monohybrid cross (one gene, two alleles), the classic Mendel ratios are:
- Homozygous dominant (AA) × Homozygous dominant (AA) = all AA - Heterozygous (Aa) × Heterozygous (Aa) = 1 AA : 2 Aa : 1 aa (3:1 phenotype ratio) - Heterozygous (Aa) × Homozygous recessive (aa) = 1 Aa : 1 aa (1:1 ratio, test cross)
In this calculator, '2 dominant alleles' = AA (homozygous dominant), '1 dominant allele' = Aa (heterozygous/carrier), '0 dominant alleles' = aa (homozygous recessive). The dominant phenotype is expressed when at least one dominant allele is present.
Formula
Punnett Square for Monohybrid Cross:
Parent genotypes → 4 possible offspring combinations
Aa × Aa cross: A a A | AA | Aa | a | Aa | aa |
Result: 1 AA : 2 Aa : 1 aa Phenotype: 75% Dominant : 25% Recessive (3:1 ratio) Carriers (Aa): 50%
All possible crosses: AA × AA = 100% AA (all dominant) AA × Aa = 50% AA, 50% Aa (all dominant, 50% carriers) AA × aa = 100% Aa (all dominant, all carriers) Aa × Aa = 25% AA, 50% Aa, 25% aa (3:1 ratio) Aa × aa = 50% Aa, 50% aa (1:1 ratio, test cross) aa × aa = 100% aa (all recessive)
How to use this Punnett Square Calculator?
1. Enter the number of dominant alleles for Parent 1: 2=AA, 1=Aa, 0=aa. 2. Same for Parent 2. 3. See the offspring phenotype percentages, genotype ratio, and carrier percentage.
Examples: Eye color (brown=dominant, blue=recessive), tongue rolling, widow's peak, attached earlobes. Note: most real traits are polygenic (controlled by many genes), so Punnett Squares are most accurate for single-gene traits.