Calculate phenotype ratios for three-trait genetic crosses. Predict outcomes when tracking three independent genes simultaneously.
Last updated: March 2026
A trihybrid cross is a genetic cross between two individuals that differ in three traits, each controlled by a different gene. This extends the principles of Mendelian genetics to analyze the simultaneous inheritance of three independent characteristics.
While a monohybrid cross tracks one gene (producing 4 possible offspring in a 2×2 grid) and a dihybrid cross tracks two genes (16 offspring in a 4×4 grid), a trihybrid cross tracks three genes and produces 64 possible offspring combinations in an 8×8×8 conceptual space.
The classic trihybrid cross between two triple heterozygotes (AaBbCc × AaBbCc) produces the famous 27:9:9:9:3:3:3:1 phenotypic ratio, representing all eight possible phenotype combinations. This demonstrates the law of independent assortment across three genes.
Classic Trihybrid Cross: AaBbCc × AaBbCc
This is the hallmark ratio of a trihybrid cross between two triple heterozygotes. It represents the eight possible phenotype combinations from three independently assorting genes.
Each parent can produce 8 different gamete types (2³ = 8 combinations of alleles). When crossed, 8 × 8 = 64 possible offspring combinations. This assumes independent assortment of all three genes.
No, this calculator assumes independent assortment (genes on different chromosomes or far apart on the same chromosome). Linked genes don't follow these ratios and require different analysis methods.
This is the phenotypic ratio for AaBbCc × AaBbCc. 27/64 show all dominant traits, 9/64 each show two dominant + one recessive, 3/64 each show one dominant + two recessive, and 1/64 shows all recessive.
Yes! A test cross would be something like AaBbCc × aabbcc. This produces simpler ratios (1:1:1:1:1:1:1:1 for all eight phenotypes) useful for determining unknown genotypes.
A dihybrid cross tracks two genes (16 offspring, 9:3:3:1 ratio), while a trihybrid tracks three genes (64 offspring, 27:9:9:9:3:3:3:1 ratio). The principles are the same, just more complex.
They're less common than monohybrid or dihybrid crosses in controlled breeding but do occur. They're important in plant and animal breeding programs tracking multiple desirable traits simultaneously.
This calculator assumes complete dominance. With incomplete dominance or codominance, you'd see more phenotype categories (27 genotypes would produce 27 different phenotypes instead of 8).
Yes, but it gets very complex (256 offspring combinations!). For four or more genes, computer programs or simplified approaches are typically used instead of manual calculation.
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