Trihybrid Cross Calculator — Three-Trait Punnett Square & Inheritance Ratios

What is a Trihybrid Punnett Square?

The Punnett square is a simple grid that lets us visualise the inheritance of a given trait. With a monohybrid cross you deal with one trait and a 2×2 table; a dihybrid cross adds a second trait and expands to 4×4 (16 cells). A trihybrid cross goes one step further — three traits, an 8×8 grid, and 64 possible crosses.

Each parent contributes 6 alleles (two per trait) and can produce up to 8 different gametes. The result: up to 27 unique genotypes and 8 distinct phenotypes — a minimalist's nightmare, but a geneticist's playground.

How to Use the Trihybrid Cross Calculator

This calculator works only for autosomal genes inherited under simple Mendelian rules (complete dominance). Follow the steps below:

1. Name the traits (optional). Enter a descriptive label for Trait A, Trait B, and Trait C — for example "Hair type", "Eye color", "Skin tone". Labels appear in the results for easier reading.
2. Choose Parent 1 (Mother) genotypes. For each of the three traits select one of:
   • AA — Homozygous dominant: both alleles are dominant.
   • Aa — Heterozygous: one dominant, one recessive allele.
   • aa — Homozygous recessive: both alleles are recessive.
   Repeat for Trait B (BB / Bb / bb) and Trait C (CC / Cc / cc).
3. Choose Parent 2 (Father) genotypes the same way.
4. Click "Build Trihybrid Cross" and enjoy the results:
   • The full 8×8 Punnett square with color-coded phenotype groups.
   • Offspring genotype frequency — every unique genotype with its count out of 64 and percentage.
   • Phenotype and Genotype — all 8 possible phenotype classes with ratios.

How to Do a Trihybrid Cross Punnett Square

Even without a calculator, the logic follows three clear steps:

Step 1 — List each parent's gametes

For a parent with genotype AaBbCc, generate all combinations of one allele from each gene pair:

ABC, ABc, AbC, Abc, aBC, aBc, abC, abc   (8 unique gametes)

A homozygous parent (e.g., AABBCC) produces only one type of gamete — ABC — which appears in all 8 positions.

Step 2 — Build the 8×8 grid

Place Parent 1's gametes along the top (columns) and Parent 2's gametes down the left side (rows). Fill each of the 64 cells by combining the column gamete with the row gamete:

• First allele pair: one letter from the column + one from the row for gene A. Put the uppercase (dominant) letter first.
• Repeat for genes B and C.

Example: column gamete ABc + row gamete aBc gives offspring AaBBcc.

Step 3 — Count genotypes and phenotypes

Count how many times each unique genotype appears in the 64 cells, then group them by phenotype:

• A trait is dominant if the genotype contains at least one uppercase allele (A_, B_, C_).
• A trait is recessive if both alleles are lowercase (aa, bb, cc).

For a fully heterozygous cross (AaBbCc × AaBbCc) the classic phenotypic ratio is:

27 : 9 : 9 : 9 : 3 : 3 : 3 : 1

Key Facts at a Glance

Frequently Asked Questions

What does "trihybrid" mean?

The prefix tri- means three. A trihybrid organism is heterozygous for exactly three independently assorting genes — for example a plant that is AaBbCc.

Why does the Punnett square have 64 cells?

Each parent can produce up to 2³ = 8 different gametes. The grid is 8 rows × 8 columns = 64 cells.

Does the 27:9:9:9:3:3:3:1 ratio always apply?

Only when both parents are fully heterozygous (AaBbCc × AaBbCc) and all three genes assort independently. Any homozygosity in either parent changes the ratio.

Can I use this calculator for sex-linked traits?

No. This calculator assumes all three traits are located on autosomes (non-sex chromosomes) and follow simple dominant/recessive inheritance.

What are the 8 phenotype classes?

With three traits, each either dominant or recessive, there are 2³ = 8 possible phenotype combinations: all-dominant (A_ B_ C_), two-dominant one-recessive (three variants), one-dominant two-recessive (three variants), and all-recessive (aa bb cc).