Punnett Square Calculator

What is a Punnett Square?

A Punnett square is a simple graphical way of discovering all of the potential combinations of genotypes that can occur in children from the two parents. Named after Reginald C. Punnett who devised the approach, it is a visual method used in classical genetics to predict the probability of inheriting particular traits. Our Punnett Square Calculator automates these calculations so you can instantly see genotypic ratios, phenotypic ratios, and the complete 2x2 square for any single-trait cross.

The calculator works for monohybrid crosses involving one gene with two alleles. A dominant allele (represented by a capital letter, e.g., A) will express its trait even if only one copy is present, while a recessive allele (lowercase, e.g., a) only expresses its trait when two copies are inherited. By selecting the mother's and father's genotypes from the dropdown menus, the tool instantly generates the Punnett square and shows the probability of each possible outcome.

How to Use the Punnett Square Calculator

Using this tool is straightforward. Follow these simple steps:

• Select Mother's Genotype: Choose from AA (homozygous dominant), Aa (heterozygous), or aa (homozygous recessive) for the maternal parent.
• Select Father's Genotype: Choose the corresponding genotype for the paternal parent.
• View the Punnett Square: The 2x2 grid displays all possible allele combinations in the offspring.
• Check the Results: The phenotype and genotype breakdown sections show probabilities for each outcome as both ratios and percentages.

For example, if both parents are heterozygous (Aa x Aa), the calculator will show a 75% chance of the dominant phenotype appearing and a 25% chance of the recessive phenotype, following Mendel's classic 3:1 ratio. The genotype ratio will be 1:2:1 (AA:Aa:aa).

Understanding Genotype and Phenotype Ratios

The genotype refers to the genetic makeup of an organism, while the phenotype refers to the observable physical characteristics. In a monohybrid cross, the genotypic ratio describes how many offspring are expected to have each combination of alleles (AA, Aa, aa), and the phenotypic ratio describes how many will display the dominant or recessive trait.

When a dominant allele (A) is present, the phenotype will reflect the dominant trait. The recessive trait (a) only appears when the genotype is homozygous recessive (aa). This is why the phenotypic ratio can be different from the genotypic ratio. Our calculator handles both automatically, giving you a complete picture of the genetic outcomes.