What does heterozygous mean?

Heterozygous means the two alleles are different, like Aa.

Why does a dihybrid cross use a 4×4 Punnett square?

A dihybrid cross tracks two genes at once. Each parent can make up to four gamete combinations (AB, Ab, aB, ab), so the square is 4×4.

Can I use different allele letters like R/r?

Yes. Change the allele letters in Trait settings and the genotype dropdowns will update automatically.

Punnett Square Calculator | Monohybrid & Dihybrid (2×2, 4×4) with Ratios

Use our Punnett Square Calculator to solve monohybrid (2×2) and dihybrid (4×4) crosses fast. Enter each parent’s genotype and the tool auto-generates gametes, fills the square, and reports genotype and phenotype ratios with percentages. Includes step-by-step explanations, clickable cell highlighting, optional phenotype labels, quick-pick crosses (Aa×Aa, AA×aa, AaBb×AaBb), and clean visuals—perfect for Mendelian genetics homework, quizzes, and AP/college biology exam prep.

Punnett Square Calculator Overview

Functionality: An interactive tool for calculating offspring genotype and phenotype probabilities for monohybrid (one trait) and dihybrid (two traits) crosses.
Key Features:
- Auto-generates gametes based on parent genotypes.
- Visual 2×2 (monohybrid) or 4×4 (dihybrid) grid generation.
- Step-by-step breakdown of results.
- Customizable allele letters and phenotype labels.
Calculation Logic:
- Gamete Formation: Each parent contributes one allele per gene.
- Grid Filling: Rows and columns represent parent gametes; cells represent combined offspring alleles.
- Probability Formula: $P = (\text{count} / \text{total}) \times 100%$.
- Phenotype Rule: Dominant phenotype is expressed if at least one dominant allele is present.
Common Cross Examples:
- Monohybrid (Aa × Aa): Genotype ratio 1:2:1; Phenotype ratio 3:1.
- Test Cross (Aa × aa): 1:1 ratio (50% dominant, 50% recessive).
- Dihybrid (AaBb × AaBb): Classic independent assortment phenotype ratio of 9:3:3:1.
Terminology:
- Heterozygous: Possessing two different alleles for a trait (e.g., Aa).
- Dihybrid Grid: Uses a 4×4 layout because heterozygous parents for two traits produce four possible gamete combinations (AB, Ab, aB, ab).

Punnett Square Calculator Overview

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