Punnett Square Calculator
Enter two parent genotypes, such as Aa and Aa, to build a monohybrid Punnett square. The grid shows every offspring combination plus the genotype and phenotype ratios.
How to use a Punnett square
- Enter each parent as a two-letter genotype, for example Aa, BB or aa.
- Use an upper-case letter for the dominant allele and lower case for recessive.
- Read the 2x2 grid, the genotype ratio and the dominant to recessive phenotype split.
Examples
Heterozygous cross
Aa x Aa
1 AA : 2 Aa : 1 aa, phenotype 3 dominant : 1 recessive
Homozygous cross
AA x aa
All Aa, phenotype 4 dominant : 0 recessive
Frequently asked questions
What is a Punnett square?
A Punnett square is a grid that predicts the possible genotypes of offspring from a cross. Each parent contributes one allele to every gamete, and the grid pairs them.
What does Aa crossed with Aa give?
A heterozygous cross gives a 1:2:1 genotype ratio of AA to Aa to aa, and a 3:1 phenotype ratio of dominant to recessive offspring.
How should I write a genotype?
Use two letters of the same trait, with an upper-case letter for the dominant allele and lower case for the recessive allele, for example Bb or bb.
What is the difference between genotype and phenotype?
Genotype is the allele pair an organism carries, such as Aa. Phenotype is the visible trait. One dominant allele is enough to show the dominant phenotype.
Does this handle a dihybrid cross?
No. This tool covers a single gene, which is a monohybrid cross. A dihybrid cross tracks two genes at once and uses a larger four by four grid.
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