Punnett Square Calculator
Predict the genotype and phenotype ratios of offspring from a genetic cross. Select each parent's genotype for one or two traits, and this calculator generates all possible offspring combinations with their probabilities.
A Punnett Square is a simple grid used to predict the genetic makeup of offspring from two parents. It was developed by Reginald Punnett in the early 1900s and is one of the most fundamental tools in genetics.
How it works: Each parent contributes one allele per trait. If a parent is heterozygous (Aa), they have a 50/50 chance of passing either allele. The Punnett Square maps out every possible combination.
Classic example (Aa x Aa cross):
- 25% chance: AA (homozygous dominant)
- 50% chance: Aa (heterozygous, carrier)
- 25% chance: aa (homozygous recessive)
- Phenotype ratio: 3 dominant : 1 recessive (75%:25%)
This is why two brown-eyed parents who each carry the blue-eye gene (Bb x Bb) have a 25% chance of having a blue-eyed child.
Dihybrid crosses look at two traits simultaneously. When both parents are heterozygous for both traits (AaBb x AaBb), the classic 9:3:3:1 phenotype ratio appears: 9/16 show both dominant traits, 3/16 show the first dominant and second recessive, 3/16 show the first recessive and second dominant, and 1/16 show both recessive traits.
Limitations: Punnett Squares assume simple Mendelian inheritance with complete dominance. Many real-world traits involve incomplete dominance, codominance, multiple alleles (like blood type), polygenic inheritance (like height or skin color), or sex-linked genes that do not follow these simple patterns.