All calculatorsTrihybrid Cross Calculator – Punnett Square
Solve three-trait (trihybrid) genetic crosses using Punnett squares. Auto-generate parent gametes, compute genotype + phenotype frequencies, and see a compact phenotype heatmap plus a probability (product rule) breakdown — with an optional full 8×8 Punnett square.
Background
A trihybrid cross tracks three independent genes (e.g., A/a, B/b, C/c). Each heterozygous gene doubles the number of gamete types. With three heterozygous genes, each parent can make up to 2³ = 8 gametes, producing 8×8 = 64 possible offspring genotypes.
How to use this calculator
- (Optional) Set allele letters and phenotype labels for each trait.
- Enter Parent 1 and Parent 2 genotypes (three gene pairs total).
- Choose which outputs you want (heatmap, product rule, genotype table, full square).
- Click Calculate to generate the results.
How this calculator works
- Gametes: each parent forms gametes containing one allele per gene.
- Grid: rows are Parent 1 gametes; columns are Parent 2 gametes.
- Fill: each cell combines the alleles from one row + one column.
- Count: tally genotypes and phenotypes to get ratios and %.
- Product rule: compute each gene as a 2×2 cross, then multiply probabilities.
Formula & Equation Used
Probability: P = (count / total) × 100%
Dominance rule (complete dominance): dominant phenotype occurs if at least one dominant allele is present.
Example Problem & Step-by-Step Solution
Example 1 — Classic trihybrid: AaBbCc × AaBbCc
Each parent can make 8 gametes (ABC, ABc, AbC, Abc, aBC, aBc, abC, abc), so there are 64 outcomes. With independent assortment and complete dominance, the phenotype ratio is 27 : 9 : 9 : 9 : 3 : 3 : 3 : 1.
Example 2 — Trihybrid testcross: AaBbCc × aabbcc
The homozygous recessive parent (aabbcc) makes only one gamete (abc), so the grid shrinks to 8×1. You’ll see 8 equally likely phenotypes (each 1/8) when the other parent is heterozygous at all three genes.
Frequently Asked Questions
Q: Why isn’t my square always 8×8?
If a parent is homozygous at one or more genes, they make fewer unique gametes (e.g., AABBCC makes only ABC), so the square becomes smaller than 8×8.
Q: What if my traits aren’t completely dominant?
This calculator uses complete dominance for phenotype labeling. Genotype counts are still correct, but phenotype interpretation may differ for incomplete dominance or codominance.
Q: Can I label traits like “Round vs Wrinkled”?
Yes. Add phenotype labels in Trait settings and the heatmap + product-rule view will display your friendly labels.
