🔬 Dihybrid Cross Calculator – Punnett Square
Cross two parents for two traits at once and see the full 16-box Punnett square breakdown of expected offspring genotypes and phenotypes.
What this calculator does
The Dihybrid Cross Calculator predicts the expected genotype and phenotype ratios among offspring when parents are crossed for two independent traits at once (for example, seed shape and seed color, following Gregor Mendel’s classic pea experiments).
How it works
Each parent’s genotype for each trait (homozygous dominant, heterozygous, or homozygous recessive) is broken down into the possible gametes it can produce. The calculator then builds the full 16-combination Punnett square by pairing every gamete from Parent 1 with every gamete from Parent 2, and tallies how many of the resulting offspring show each combination of dominant and recessive traits.
- When both parents are heterozygous for both traits (AaBb × AaBb), this produces the classic 9:3:3:1 phenotype ratio.
- Different starting genotypes produce different ratios, which this calculator computes exactly.
A note on accuracy
This calculator assumes the two traits are controlled by genes on different chromosomes (or far enough apart to assort independently), following Mendel’s law of independent assortment. Traits controlled by linked genes, multiple genes, or environmental factors will not follow these simple ratios. This tool is intended for general biology education.