Punnett Square Calculator
Trihybrid cross — predict offspring genotype and phenotype probabilities for three independent traits.
💡 Quick Summary
Predict offspring genotype and phenotype probabilities for a trihybrid (three-trait) cross. Select or enter parental genotypes for three independent traits, define your allele symbols, and instantly see the 8×8 Punnett square (64 cells), all unique genotypes, the classic 27:9:9:9:3:3:3:1 phenotypic ratio, and researcher-grade insights including parental gametes, phenotype distribution chart, heterozygosity metrics, chi-square goodness-of-fit, and expected offspring counts.
📋 How to Use
- Select preset genotypes for Traits 1, 2, and 3 for the Mother using the radio buttons, or type a full 6-character custom genotype (e.g. AaBbCc) in the custom input field.
- Repeat for the Father in the same way.
- Confirm the allele symbols: enter the dominant and recessive letter for each of the three traits. All six symbols must be unique single characters.
- All results update automatically as you type or select options.
- Scroll to the Researcher Insights sections to explore parental gametes (up to 8 per parent), heterozygosity metrics, and chi-square analysis.
- Enter Total offspring (N) to calculate expected counts per phenotype class.
- Click Download results as PDF to open a print-ready version of all results.
- Click Clear all changes to reset to the default AaBbCc × AaBbCc cross.
🧮 Formulas & Logic
📊 Result Interpretation
The classic result of an AaBbCc × AaBbCc cross assuming complete dominance and independent assortment. Arises by multiplying three independent 3:1 monohybrid ratios: (3:1)³ = 27:9:9:9:3:3:3:1.
If both parents are fully homozygous at all three loci (e.g. AABBCC × aabbcc), all 64 offspring cells are identical trihybrids.
When one or more parents are homozygous at a locus, the number of unique phenotype classes is reduced — a homozygous locus contributes no phenotypic variation.
No significant deviation from expected Mendelian ratios. Your data are consistent with independent assortment of three traits.
Significant deviation detected. Consider genetic linkage between traits, natural selection, small sample size, or non-Mendelian mechanisms.
🔬 Applications
- Predicting phenotype class frequencies in F₂ and test-cross generations of three-gene experiments
- Teaching Mendel's Law of Independent Assortment for three simultaneously segregating genes
- Agricultural genetics — planning crosses involving three independently assorting traits (e.g. seed colour, seed texture, plant height)
- Genetic counselling — estimating offspring probability for combinations of three recessive conditions
- Experimental design — calculating minimum sample sizes to detect all 8 phenotype classes with statistical confidence
- Chi-square testing — assessing whether observed phenotype frequencies match theoretical Mendelian predictions
⚠️ Common Mistakes & Warnings
All three genes are treated as unlinked — located on different chromosomes or far apart on the same chromosome. Linked genes produce non-standard gamete frequencies and offspring ratios that deviate from the 27:9:9:9:3:3:3:1 pattern.
The phenotype model assumes complete dominance: any organism carrying at least one dominant allele expresses the dominant phenotype. Codominance, incomplete dominance, and epistatic interactions between loci are not modelled.
Each phenotype class needs an expected count ≥ 5. For the 27:9:9:9:3:3:3:1 ratio, the rarest class (aabbcc = 1/64) requires N ≥ 320 offspring. For reliable power, N ≥ 640 is recommended.
