Trihybrid cross calculator.
Work out a three-gene cross. Choose each parent genotype for three independent genes and the calculator returns the eight-class offspring phenotype ratio.
Parent genotypes
LiveUppercase letters are dominant alleles, lowercase recessive. The three genes assort independently, so the cross is the product of three single-gene crosses over 64 boxes.
Phenotype ratio
27 : 9 : 9 : 9 : 3 : 3 : 3 : 1
8 trait classes, out of 64
A three-gene cross assuming independent assortment and simple dominance. Calculations run in your browser; nothing you enter is stored.
How it works
Three genes at once
A trihybrid cross follows three genes through one mating. As with two genes, independent assortment means each gene acts as its own cross, and the combined outcome is the product of all three.
Crossing AaBbCc with AaBbCc gives a 3:1 split per gene, and multiplying three of them produces the eight-class 27:9:9:9:3:3:3:1 ratio over 64 equally likely combinations.
Reference
Common trihybrid crosses.
The offspring phenotype ratio, out of 64, for three-gene parent genotypes.
| Cross | Phenotype ratio |
|---|---|
| AaBbCc x AaBbCc | 27 : 9 : 9 : 9 : 3 : 3 : 3 : 1 |
| AaBbCc x aabbcc | 8 : 8 : 8 : 8 : 8 : 8 : 8 : 8 |
| AABbCc x AaBbCc | 36 : 12 : 12 : 0 : 4 : 0 : 0 : 0 |
The full guide
The complete guide to trihybrid crosses.
What a trihybrid cross is, where 27:9:9:9:3:3:3:1 comes from, and how to read it.
What is a trihybrid cross?
A trihybrid cross tracks three genes at the same time. Each parent carries two alleles for each of the three genes and passes one of each to every offspring, so the maths follows the same independent-assortment rule as a dihybrid cross, just with one more gene.
Triple heterozygotes, AaBbCc, are the usual starting point because they give the clean reference ratio.
Where 27:9:9:9:3:3:3:1 comes from
Each gene on its own gives a 3:1 phenotype split. Multiply three of those 3:1 ratios and you get eight classes: 27 showing all three dominant traits, three groups of 9 with two dominant and one recessive, three groups of 3 with one dominant and two recessive, and a single all-recessive class, out of 64.
Those 64 boxes are the trihybrid Punnett square, and every cell is equally likely.
Reading the ratio
The eight numbers count the trait classes out of 64, from all-dominant down to all-recessive. Divide any count by 64 to get its percentage; the all-dominant class is about 42% and the all-recessive class about 1.6%.
As always these are expected long-run proportions, not a promise for one litter or batch of seeds.
Keeping it manageable
A full trihybrid Punnett square has 64 cells, which is why the multiply-the-genes shortcut is so useful. The calculator does it instantly for any combination of parent genotypes.
For one or two genes, use the Punnett square or dihybrid cross calculators instead.
The formula
Three genes,
eight classes.
A trihybrid cross is the product of three single-gene crosses, giving 27:9:9:9:3:3:3:1 from AaBbCc by AaBbCc.
Dihybrid cross ›# Trihybrid (three genes)
ratio = geneA × geneB × geneC
# AaBbCc x AaBbCc
27 : 9 : 9 : 9 : 3 : 3 : 3 : 1Questions
Trihybrid questions.
How do I calculate a trihybrid cross?
+
Treat each of the three genes as its own cross, then multiply the three results. Set both parent genotypes above and the calculator does it for you.
Why is the trihybrid ratio 27:9:9:9:3:3:3:1?
+
Because each gene gives a 3:1 split, and multiplying three 3:1 ratios produces eight phenotype classes in those proportions over 64 boxes.
How many boxes are in a trihybrid Punnett square?
+
Sixty-four. Each parent makes eight gamete types, and 8 times 8 is 64 equally likely combinations.
Does this assume independent assortment?
+
Yes. The ratio assumes the three genes are inherited independently with simple dominance. Linked genes need a different model.
Is this trihybrid cross calculator free?
+
Yes. It is completely free with no sign-up, and every calculation runs locally in your browser, so nothing you enter is stored or sent anywhere.
About the developer
Jean Borg
Jean builds and maintains every calculator on freecalculators.pro from Malta, with a focus on tools that are fast, free and show their working. The trihybrid cross calculator covers three-gene crosses with independent assortment, for education.