# Punnett Trihybrid & Dihybrid Cross Visualizer

Compute 2-3 gene Mendelian crosses with a full Punnett square and forked-line branch diagram. Supports complete, incomplete and codominance inheritance.

> Canonical page: https://elysiatools.com/en/tools/punnett-trihybrid-cross

- **Category:** Education

- **Keywords:** punnett square, trihybrid, dihybrid, mendelian genetics, cross, forked line, genotype ratio, phenotype ratio, genetics, biology

## Overview

Compute **2-gene (dihybrid)** and **3-gene (trihybrid)** Mendelian crosses with a full Punnett square AND a forked-line (branch) diagram.

This extends the [Mendelian Punnett Square](#/tools/mendelian-punnett-square) tool to multiple loci: that tool handles single-gene crosses, this one handles **2-3 genes simultaneously**.

**How to use**
1. Declare each gene on its own line: `Trait = Allele1,Allele2 [mode]`
   - `mode` is optional, default `complete`. Choices: `complete` / `incomplete` / `codominance`.
   - Example: `Seed color = Y,y` · `Seed shape = R,r [complete]` · `Flower = R,W [incomplete]`
2. Enter both parents' genotypes, e.g. `YyRr` (dihybrid) or `AaBbCc` (trihybrid). The tool matches allele letters to each declared gene.
3. Choose the display: Punnett square + ratios, forked-line branch diagram, or both.

**What you get**
- **Punnett square**: the full 2ⁿ × 2ⁿ grid (4×4 for dihybrid, 8×8 for trihybrid).
- **Forked-line diagram**: the branch method showing how each gene's monohybrid ratio (e.g. 1:2:1) multiplies into the final multi-gene distribution — the classic way to solve trihybrid crosses without drawing a 64-cell grid.
- **Genotype ratio**: every unique genotype tallied with count and percentage.
- **Phenotype ratio**: after applying each gene's inheritance mode (complete/incomplete/codominance).

**Inheritance modes**
- *Complete*: uppercase allele masks lowercase (Aa looks like AA).
- *Incomplete*: heterozygote is a blend (RW → "RW-blend", e.g. pink flowers from red + white).
- *Codominance*: both alleles expressed (AB blood type, spots).

## Inputs

- **Genes (one per line: Trait = Allele1,Allele2 \[mode\])** (textarea): Declare 2 or 3 genes, one per line. Format: Trait = Allele1,Allele2 \[mode\]. Mode is optional (default complete).
- **Parent 1 genotype (e.g. AaBb or AaBbCc)** (text): Parent 1 genotype. Use the same letters as declared in the genes above.
- **Parent 2 genotype** (text): Parent 2 genotype.
- **Display** (select): Both shows the full grid and the branch diagram. Punnett shows only the grid + ratios. Forked shows only the branch method.
- **Sort** (select): How to sort the genotype and phenotype ratio lists.

## When to use

- When analyzing multi-locus Mendelian crosses (dihybrid or trihybrid) without manually drawing complex 16-cell or 64-cell Punnett squares.
- When teaching or studying genetics to compare the Punnett square grid method with the mathematical forked-line branch method.
- When calculating offspring genotype and phenotype ratios for traits involving non-Mendelian inheritance like incomplete dominance or codominance.

## How it works

- Define your genes by entering each trait, its alleles, and its inheritance mode (complete, incomplete, or codominance) on a new line.
- Input the genotypes of both parents using the designated allele letters (e.g., YyRr or AaBbCc).
- Select your preferred display option (Punnett square, forked-line diagram, or both) and choose how to sort the resulting ratios.
- Generate the results to view the interactive grid, branching diagram, and calculated genotype and phenotype percentages.

## Use cases

- Generating a 64-cell trihybrid Punnett square for biology classroom presentations and worksheets.
- Verifying expected phenotypic ratios for dihybrid crosses involving mixed inheritance modes, such as one complete dominance trait and one incomplete dominance trait.
- Demonstrating the branch method (forked-line diagram) to genetics students to simplify multi-gene probability calculations.

## Frequently asked questions

### Can this tool handle more than three genes?

No, this tool is specifically designed for 2-gene (dihybrid) and 3-gene (trihybrid) crosses.

### What is the difference between the Punnett square and the forked-line diagram?

The Punnett square displays the full grid of allele combinations, while the forked-line diagram uses branching probability lines to calculate multi-gene ratios without a large grid.

### How do I specify incomplete dominance or codominance?

Add [incomplete] or [codominance] at the end of your gene definition line, for example: Flower = R,W [incomplete].

### What happens if I enter invalid parent genotypes?

The tool requires parent genotypes to match the allele letters declared in your gene definitions; mismatched letters will cause calculation errors.

### How are the phenotype ratios sorted?

You can sort the genotype and phenotype ratio lists either by frequency (highest percentage first) or alphabetically.

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