Trihybrid Cross Punnett Square Calculator
Enter two parent genotypes — e.g. AaBbCc × AaBbCc — and get the full 64-box Punnett grid, the 27:9:9:9:3:3:3:1 phenotypic ratio, exact genotype probabilities, and a phenotype-probability query tool. Everything runs in your browser.
1. Enter the cross
Uppercase = dominant allele, lowercase = recessive allele. Exactly three gene pairs, each pair the same letter (e.g. AaBbCc).
2. Name the traits (optional)
Results
Punnett grid
Phenotypic ratio
Genotypic ratio
Phenotype probability query
What is the probability of a specific phenotype in the cross above? Pick dominant / recessive / any per gene.
How it works
Each parent produces 23 = 8 gamete types: an AaBbCc parent makes ABC, ABc, AbC, Abc, aBC, aBc, abC, abc — each with probability 1/8. Crossing the two gamete lists gives an 8 × 8 = 64-box grid. Every box is equally likely, so probabilities are exact box counts: e.g. 27 of 64 boxes = 27/64 = 42.1875%. The calculator assumes independent assortment (genes on different chromosomes) and complete dominance.
Frequently asked questions
What is a trihybrid cross?
A trihybrid cross is a genetic cross in which the two parents differ at three genes — for example AaBbCc crossed with AaBbCc. Because each gene assorts independently, every parent produces 2³ = 8 different gamete types, and the Punnett square has 8 × 8 = 64 boxes. In the classic case AaBbCc × AaBbCc the offspring phenotypes follow the famous 27:9:9:9:3:3:3:1 ratio.
How many gametes does an AaBbCc parent produce?
Eight: ABC, ABc, AbC, Abc, aBC, aBc, abC, and abc. Each gamete carries one allele copy from each of the three genes, so there are 2 × 2 × 2 = 8 combinations. Under independent assortment each gamete is equally likely (1/8 = 12.5%). A homozygous parent like AABBCC still “produces” 8 gametes, but all 8 are the same combination (ABC).
What is the 27:9:9:9:3:3:3:1 phenotypic ratio?
It is the expected phenotype distribution of the classic trihybrid cross AaBbCc × AaBbCc: 27 of 64 offspring (42.1875%) show all three dominant traits; three phenotypes each cover 9 of 64 (14.0625%); three phenotypes each cover 3 of 64 (4.6875%); and 1 of 64 (1.5625%) shows all three recessive traits. It is simply the product of three independent 3:1 monohybrid ratios: (3:1) × (3:1) × (3:1).
What is the probability of one specific phenotype, for example all-recessive aabbcc?
In the classic cross AaBbCc × AaBbCc, the all-recessive phenotype fills exactly 1 of the 64 Punnett boxes, so the probability is 1/64 = 1.5625%. Use the phenotype-probability query below this calculator to get the exact fraction and percentage for any combination of dominant and recessive traits in your own cross.
What does a trihybrid testcross (AaBbCc × aabbcc) produce?
Eight phenotypes in a 1:1:1:1:1:1:1:1 ratio. Each of the eight gamete types of the triple-heterozygote parent pairs with the single abc gamete of the homozygous-recessive parent, so every phenotype appears in exactly 8 of the 64 boxes (8/64 = 1/8 = 12.5% each). This is the trihybrid analogue of the dihybrid 1:1:1:1 testcross.
How many different genotypes can a trihybrid cross produce?
At most 27: each gene can form 3 genotypes (AA, Aa, aa), and 3 × 3 × 3 = 27. In the classic cross AaBbCc × AaBbCc all 27 actually appear. The triple heterozygote AaBbCc is the single most common genotype: it fills 8 of the 64 boxes, i.e. a probability of 8/64 = 1/8 = 12.5%.
When does the 27:9:9:9:3:3:3:1 ratio break down?
The textbook ratio only holds under ideal Mendel conditions: the three genes must assort independently (different chromosomes or far apart, no linkage), dominance must be complete, and there must be no epistasis, lethal alleles, or sex linkage. It is also a large-population expectation — a single litter of 8 offspring will rarely match 27:9:9:9:3:3:3:1 exactly.
Can I use my own trait names in this calculator?
Yes. Under the genotype inputs you can label the dominant and recessive trait for each of the three genes. The defaults are Mendel-style seed and flower traits: Round vs Wrinkled seeds, Yellow vs Green seeds, and Purple vs White flowers. The ratio mathematics does not depend on the names.
What is the difference between a trihybrid and a dihybrid cross?
A dihybrid cross tracks two genes (16-box Punnett square, classic 9:3:3:1 ratio); a trihybrid cross tracks three genes (64-box grid, classic 27:9:9:9:3:3:3:1 ratio). If your cross involves only one or two genes, use the dedicated dihybrid cross Punnett square calculator at nrtechstudio.com/dihybrid-cross-punnett-square/ — it also includes a monohybrid mode.
How does this calculator compute exact probabilities?
By brute-force enumeration, not simulation: it lists all 8 gametes of each parent, combines them into all 64 offspring boxes, and counts how many boxes match each genotype and phenotype. Every probability is an exact box count (e.g. 27/64 = 42.1875%), with no rounding error, computed entirely in your browser.
Free tool by NRTechStudio