Punnett Square Calculator
Free Punnett square generator for monohybrid (2×2), dihybrid (4×4), trihybrid (8×8), and quadhybrid (16×16) crosses — plus special modes for X-linked traits, ABO blood type, incomplete dominance, and codominance. Generate any Punnett square instantly with genotype ratios, phenotype ratios, probability summaries, and step-by-step working.
Select a cross type, enter parent genotypes, and click Generate to build the complete Punnett square with genotype/phenotype ratios and probabilities.
⚠️ This calculator assumes independent assortment (Mendel's Law — genes on different chromosomes). The four-allele 4×4 grid contains 16 combinations.
⚠️ Performance note: The 8×8 trihybrid grid contains 64 combinations across 27 genotype classes. Rendering may take 1–2 seconds on older devices.
⚠️ Warning: This will generate a 16×16 grid with 256 combinations across 81 genotype classes and 16 phenotype classes. This is computationally intensive — click Generate to proceed. Use the zoom controls to navigate the grid on smaller screens.
🔬 X-linked traits are carried on the X chromosome. Males (XY) show the trait with only one copy; females (XX) need two copies to show a recessive trait.
🩸 ABO Blood Type uses three alleles: IA, IB, and i. IA and IB are codominant; i is recessive to both. Select parent blood types below.
🌸 Incomplete dominance: The heterozygous phenotype is a blend of both homozygous phenotypes. Neither allele is fully dominant. Classic example: Red × White → Pink.
🐄 Codominance: Both alleles are fully expressed simultaneously in the heterozygote. No blending — both phenotypes appear side by side. Classic example: Roan cattle (red + white patches).
🧬 Autosomal Dominant/Recessive Disease Risk. Select a disease preset or enter custom inheritance type and parental carrier status.
What Is a Punnett Square?
A Punnett square (also called a genetics box diagram, Punnett diagram, or heredity square) is a grid tool used to predict the probability of offspring inheriting specific traits from two parents. It was invented by British geneticist Reginald Crundall Punnett (1875–1967) in the early twentieth century to visualize Mendelian inheritance patterns systematically.
The Punnett square is grounded in Mendel's two foundational laws: the Law of Segregation (each parent passes one allele per gene to each offspring) and the Law of Independent Assortment (genes on different chromosomes are inherited independently). By listing each parent's possible gametes along the top and side of the grid, every cell represents one possible offspring genotype with equal probability.
The punnett square generator on this page handles every cross type: simple dominant/recessive (monohybrid), two-trait crosses (dihybrid), three-trait crosses (trihybrid), four-trait quadhybrid crosses, and special inheritance patterns including X-linked traits, ABO blood type with multiple alleles, incomplete dominance, and codominance.
Generate Any Punnett Square Instantly — Mono, Di, Tri & Quadhybrid Crosses
This punnett square solver automatically generates the correct grid for any number of traits. The five modes cover every cross type taught in genetics from introductory biology through advanced genetics courses. Simply enter the parent genotypes, click Generate, and receive a complete visual grid plus genotype ratios, phenotype ratios, probability summaries, and a downloadable PNG.
How to Make a Punnett Square (Step-by-Step)
Learning how to make a Punnett square is one of the most important skills in introductory genetics. Follow this six-step method for a monohybrid cross Punnett square:
Example: Tall (Tt) × Short (tt)
- Step 1 — Write parent genotypes: Parent 1 = Tt (heterozygous tall), Parent 2 = tt (homozygous short). T = dominant (tall), t = recessive (short).
- Step 2 — Identify gametes: Parent 1 (Tt) produces two gametes:
Tandt. Parent 2 (tt) produces:tandt. - Step 3 — Draw a 2×2 grid: Write Parent 1 gametes across the TOP as column headers. Write Parent 2 gametes down the LEFT SIDE as row headers.
- Step 4 — Fill each cell: Each cell = column gamete + row gamete. Top-left: T+t =
Tt. Top-right: t+t =tt. Bottom-left: T+t =Tt. Bottom-right: t+t =tt. - Step 5 — Count results: Genotypes: Tt, tt, Tt, tt → ratio 1:1. Phenotypes: 2 tall : 2 short → 50% tall, 50% short.
- Step 6 — Interpret probabilities: 50% chance offspring is tall (Tt), 50% chance short (tt).
⚠️ Common mistake: Students often forget to separate BOTH alleles when writing gametes. Tt produces T AND t as two separate gametes — not "Tt" as a single gamete unit.
Dihybrid Cross — How to Make a 4×4 Punnett Square with 2 Traits
A two trait Punnett square (dihybrid cross) studies TWO genes simultaneously. Based on Mendel's Law of Independent Assortment, it requires a 4×4 Punnett square with 16 cells (4 gametes × 4 gametes). The 4x4 Punnett square is the most commonly requested grid in high school and university genetics.
How to Determine Gametes for AaBb (the FOIL method)
A parent with genotype AaBb can produce four gamete types by combining one allele from each locus: AB, Ab, aB, ab. These four gametes become the column and row headers of the 4×4 grid.
Classic Mendel Dihybrid Cross: AaBb × AaBb
A = Round seeds (dominant), a = wrinkled (recessive). B = Yellow (dominant), b = green (recessive).
- Each parent produces 4 gametes: AB, Ab, aB, ab
- Build a 4×4 grid — 16 cells total
- Count phenotype classes from the 16 cells
Use the Dihybrid (4×4) tab above to generate this grid instantly with all 16 cells, genotype frequency table, phenotype ratios, and probability summary. This is how to make a Punnett square with 2 traits the fast way.
Quadhybrid Cross — The 16×16 Punnett Square (4 Traits)
A quadhybrid cross tracks FOUR traits simultaneously. It requires a 16×16 Punnett square with 256 cells — far too large to draw by hand reliably. This punnett square 16 box generator is one of the only tools online that calculates and displays the complete 16 by 16 Punnett square with all 256 combinations.
All 16 Gametes for AaBbCcDd:
aBCD, aBCd, aBcD, aBcd, abCD, abCd, abcD, abcd 2⁴ = 16 gamete types from a quadruple-heterozygous parent
| Metric | Value | Formula |
|---|---|---|
| Total gamete types | 16 | 2⁴ |
| Total cells in grid | 256 | 4⁴ |
| Unique genotype classes | 81 | 3⁴ |
| Phenotype classes | 16 | 2⁴ |
💡 How to do a Punnett square with 4 traits by hand is essentially impossible — 256 cells with 81 unique genotype classes makes manual calculation extremely error-prone. Use the Quadhybrid (16×16) tab above to generate the complete punnett square 16 boxes grid instantly with all ratios calculated automatically.
Standard Phenotypic Ratio for AaBbCcDd × AaBbCcDd:
The probability formula for any phenotype class in an n-trait cross: P = (3/4)^d × (1/4)^r where d = number of traits showing dominant phenotype and r = number showing recessive phenotype.
Multiple Alleles — ABO Blood Type Punnett Square
Most traits have only two alleles, but some genes have multiple alleles. ABO blood type is the classic example: it has three alleles — IA, IB, and i. IA and IB are codominant (both expressed equally); i is recessive to both.
| Blood Type | Possible Genotypes | Alleles Present |
|---|---|---|
| Type A | IAIA or IAi | A antigen only |
| Type B | IBIB or IBi | B antigen only |
| Type AB | IAIB | Both A and B antigens |
| Type O | ii | No A or B antigens |
Worked Example: IAi (Type A carrier) × IBi (Type B carrier)
- Parent 1 gametes: IA and i
- Parent 2 gametes: IB and i
- 2×2 grid produces: IAIB (AB), IAi (A), IBi (B), ii (O)
- Result: 25% AB, 25% A, 25% B, 25% O — all four blood types possible!
Use the Special Crosses → ABO Blood Type mode above to calculate any ABO blood type cross instantly with a complete multiple alleles Punnett square.
How to Write Genotypes and Phenotypes
Understanding genotype notation is essential before using any genotype calculator or Punnett square tool. Here are the core concepts:
- Genotype — the actual genetic code (e.g. Aa, BB, tt)
- Phenotype — the physical expression of that code (e.g. tall, brown eyes, purple flowers)
- Dominant allele — written in UPPERCASE (e.g. A, B, T)
- Recessive allele — written in lowercase (e.g. a, b, t)
- Wildcard notation — A_ means AA or Aa (any genotype showing dominant phenotype)
Gametes Explained — What the gametes Punnett square headers represent
Gametes are sex cells (sperm and egg). Each gamete carries ONE allele per locus from that parent. An Aa parent produces two gamete types: half carry A, half carry a. An AaBb parent produces four gamete types: AB, Ab, aB, ab — one combination from each locus.
| Term | Meaning | Example |
|---|---|---|
| Homozygous dominant | Two identical dominant alleles | AA, BB, TT |
| Homozygous recessive | Two identical recessive alleles | aa, bb, tt |
| Heterozygous | One dominant, one recessive | Aa, Bb, Tt |
| Dominant phenotype | At least one uppercase allele present | AA or Aa → dominant trait shown |
| Recessive phenotype | Both alleles are lowercase | aa → recessive trait shown |
Punnett Square Ratios — Complete Reference
Every standard Punnett square cross produces a predictable genotypic and phenotypic ratio. This quick reference covers all cross types supported by this punnett calculator.
| Cross Type | Grid | Cells | Genotypic Ratio | Phenotypic Ratio |
|---|---|---|---|---|
| Aa × Aa (monohybrid het × het) | 2×2 | 4 | 1:2:1 | 3:1 |
| Aa × aa (test cross) | 2×2 | 4 | 1:1 (Aa:aa) | 1:1 |
| AA × aa (pure cross) | 2×2 | 4 | all Aa | all dominant |
| AaBb × AaBb (dihybrid) | 4×4 | 16 | 9 classes | 9:3:3:1 |
| AaBbCc × AaBbCc (trihybrid) | 8×8 | 64 | 27 classes | 27:9:9:9:3:3:3:1 |
| AaBbCcDd × AaBbCcDd (quadhybrid) | 16×16 | 256 | 81 classes | 81:27:…:1 (16 classes) |