Punnett Square Calculator

Calculate the probability of inherited traits using a Punnett square. Enter parent genotypes to see genotypic and phenotypic ratios instantly.

Enter two alleles (e.g., AA, Aa, or aa)

Enter two alleles (e.g., AA, Aa, or aa)

Capital letter for dominant allele

Punnett Square: List Parent 1 gametes on top, Parent 2 on side; Each cell = combination of one gamete from each parent; Count genotypes and phenotypes for ratios
Example: Two heterozygous parents (Bb × Bb); Punnett Square: BB | Bb, Bb | bb; Genotypic ratio: BB: 1/4 (25%), Bb: 2/4 (50%), bb: 1/4 (25%); Phenotypic ratio: Dominant: 3/4 (75%), Recessive: 1/4 (25%)

What is a Punnett square and how does it work?

A Punnett square is a diagram used to predict the genetic outcomes of offspring from two parents. It works by listing all possible gametes from one parent across the top and from the other parent down the side. Each cell in the grid represents a possible genotype of the offspring, formed by combining one gamete from each parent. The square shows all possible combinations with equal probability, allowing you to calculate genotypic and phenotypic ratios.

What is the difference between genotype and phenotype?

Genotype refers to the genetic makeup of an organism (the specific alleles it carries, e.g., Bb, BB, or bb). Phenotype refers to the observable physical or biochemical characteristics that result from the genotype (e.g., brown eyes or blue eyes). For a dominant trait, both homozygous dominant (BB) and heterozygous (Bb) genotypes produce the same dominant phenotype. Only homozygous recessive (bb) shows the recessive phenotype.

What does heterozygous and homozygous mean?

Homozygous means an organism has two identical alleles for a gene (e.g., BB or bb). Homozygous dominant (BB) has two dominant alleles; homozygous recessive (bb) has two recessive alleles. Heterozygous (Bb) means the organism has two different alleles - one dominant and one recessive. In simple dominant-recessive inheritance, heterozygous individuals show the dominant phenotype but carry the recessive allele, making them "carriers" who can pass the recessive trait to offspring.

Can Punnett squares predict multiple traits at once?

Yes, but complexity increases rapidly. A monohybrid cross (one trait) uses a 2×2 square with 4 outcomes. A dihybrid cross (two traits) requires a 4×4 square with 16 outcomes. A trihybrid cross needs an 8×8 square with 64 outcomes! This calculator handles single-gene (monohybrid) crosses. For multiple independent traits, multiply the individual probabilities from separate monohybrid crosses. However, genes on the same chromosome may be linked and don't follow simple Punnett square predictions.