Trihybrid Cross Punnett Square Calculator
Explore three traits. Understand every combination.
Parent Genotypes
Cross Results Summary
8 phenotypes · 27 genotypes · 64 equally likely pairings
Phenotype Classes (8 possible)
Genotype breakdown (27)
Aggregated across all matching cells. Fractions use 64 equally weighted allele-choice paths.
| Genotype | Fraction | Probability |
|---|
Ratio positions follow the eight phenotype labels below. Zero entries mean a class cannot occur in this model. Probabilities are expectations, not a guarantee for a litter or sample.
Interactive Punnett Square
Top: Parent 1 gametes · Left: Parent 2 gametes. Select, hover or focus a cell to inspect it.
Repeated gametes are combined with their correct probabilities. The table uses the actual distinct gametes; an 8 × 8 grid occurs when both parents are heterozygous at all three loci.
Worked Example
Independent loci · Complete dominance · Random fertilization · Equal allele segregation. Linkage, recombination phase, epistasis and differing survival are not modeled.
Frequently Asked Questions
What does a trihybrid cross show?
It predicts combinations at three genetic loci from two parental genotypes. This tool uses symbolic A/a, B/b and C/c allele pairs and shows offspring genotype and phenotype probabilities.
How are the phenotype ratios calculated?
The calculator enumerates parental gametes and pairs them with probability weights. Under complete dominance, AA and Aa share the A-dominant phenotype; the same logic applies at B and C. Counts for the eight classes are reduced by their common divisor.
Does this assume independent assortment?
Yes. Genes are treated as independently inherited. Linked genes require haplotype phase and recombination frequencies, which this tool does not accept.
Can I use this for traits other than pea traits?
Yes, for a theoretical three-locus Mendelian model meeting these assumptions. Decorative peas and chromosome colors are illustrations, not validated trait-to-gene mappings or clinical predictions.
More questions (8)
What input notation is supported?
Enter six letters: two A/a alleles, two B/b alleles and two C/c alleles, in that order. Spaces are ignored and aA becomes Aa. Other locus letters, missing pairs and reordered loci are rejected to keep the selectors unambiguous.
Why does AaBbCc produce eight gametes?
Each of three heterozygous loci contributes two alternatives. Independent combinations give 2³ = 8 distinct gametes, each with probability 1/8. A homozygous locus contributes only one distinct alternative.
Why is the table smaller for some crosses?
Only distinct gametes are shown. AaBbCc × aabbcc gives eight columns and one row, with each cell probability 1/8. Duplicate homozygous allele choices are combined rather than displayed as identical rows.
Is one AaBbCc cell the same as the total AaBbCc chance?
No. In the classic cross one cell is 1/64, while eight cells yield AaBbCc. The total genotype probability is 8/64 = 12.5%. The selected-cell panel shows both values.
When does the 27:9:9:9:3:3:3:1 ratio apply?
For AaBbCc × AaBbCc with independent assortment, complete dominance at all three loci, random fertilization and no viability differences. It comes from multiplying the three separate 3:1 phenotype ratios.
How do I verify a calculation manually?
Draw three 2 × 2 single-locus crosses. Multiply the probabilities for an A genotype, a B genotype and a C genotype to find the combined genotype probability. Add genotypes sharing the same dominant/recessive phenotype.
Are these measured offspring counts or probabilities?
Probabilities. Fractions out of 64 are equally weighted allele-choice paths, not a claim that you have 64 offspring. Small real samples can differ from the expected distribution.
Can this calculate incomplete dominance or human disease risk?
The phenotype classification here assumes complete dominance. It does not support codominance, epistasis, penetrance, sex-linked inheritance or clinical diagnosis. Use an appropriate model and specialist advice for real disease risk.
Sources & References
NCBI / National Library of MedicineGenetics: inheritance patterns and model limitations
Nature Education · ScitableMendelian inheritance and independent assortment
Educational Mendelian model · No institutional endorsement
Explore three-locus Mendelian crosses with an interactive Punnett square, weighted gametes, phenotype ratios and aggregated genotype probabilities.