Create mono- and dihybrid Punnett squares. Calculate genotype and phenotype ratios with interactive allele selection.
The Punnett square generator turns a genetic cross into the classic grid: you set each parent's genotype (one gene for a monohybrid cross, two for a dihybrid), the tool splits each parent into its possible gametes, and fills every cell with the offspring genotype formed when one gamete from each parent fuses. It then tallies the genotype ratio and, using the dominance rules you specify, the phenotype ratio. The thing that trips people up most: a cross like Aa x Aa yields a 1:2:1 genotype ratio, not the 3:1 they half-remember from class. The 3:1 is the phenotype ratio - the 1:2:1 counts genotypes.
A concrete input and expected output from the current implementation.
Input
Monohybrid cross. Parent 1 genotype: Aa. Parent 2 genotype: Aa. A is completely dominant over a.
Expected output
2x2 grid with cells AA, Aa, Aa, aa. Genotype ratio: 1 AA : 2 Aa : 1 aa. Phenotype ratio: 3 dominant (A_) : 1 recessive (aa).
Each parent forms gametes A and a in equal proportions, so the four cells are equally likely offspring. Both AA and Aa show the dominant phenotype because A masks a, leaving three dominant-phenotype cells and one recessive.
For a monohybrid cross the tool writes each parent's two alleles along the top and side of a 2x2 grid. For a dihybrid cross it first combines each parent's allele pairs into every possible gamete (RrYy produces RY, Ry, rY, ry) for a 4x4 grid. Each cell holds the genotype formed by fusing its row gamete with its column gamete, with equivalent pairings written identically.
The tool counts how many cells share each genotype and reports the ratio in lowest terms, then groups genotypes into phenotypes according to the dominance pattern you set. With complete dominance, AA and Aa collapse into one dominant class. With incomplete dominance or codominance, each genotype is its own phenotype, so the phenotype ratio matches the genotype ratio.
No. The ratio is the expectation across a very large number of offspring, like the long-run average of a coin flip. A small family can easily land on 2:2, 4:0, or any other split. The tool predicts proportions across a population of offspring, not the outcome of any particular pregnancy.
Real traits often involve several genes, incomplete dominance, sex linkage, or genes on the same chromosome. A single-gene square captures only the simplest inheritance, so if your observed offspring deviate strongly from the grid, one of those complications is usually at work rather than the square being wrong.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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