Dihybrid Cross Calculator
Two-Trait Punnett Square Generator
Select parent genotypes for both traits to calculate offspring probabilities and visualize the 4×4 genetic cross.
Working with two genetic traits? This 4×4 Punnett Square calculator helps you predict offspring genotype probabilities for dihybrid crosses.
Maternal Genotype (♀)
Paternal Genotype (♂)
Offspring Genotype Probabilities
4×4 Punnett Square
| ♂ \ ♀ | AB | Ab | aB | ab |
|---|---|---|---|---|
| AB | AABB | AABb | AaBB | AaBb |
| Ab | AABb | AAbb | AaBb | Aabb |
| aB | AaBB | AaBb | aaBB | aaBb |
| ab | AaBb | Aabb | aaBb | aabb |
💡 Single-trait analysis? Check out the simpler monohybrid Punnett Square calculator for single-gene inheritance.
| Result | Genotype | Phenotype |
|---|---|---|
| AABB | AABB | AB |
| AABb | AABb | AB |
| AaBB | AaBB | AB |
| AaBb | AaBb | AB |
| AAbb | AAbb | Ab |
| Aabb | Aabb | Ab |
| aaBB | aaBB | aB |
| aaBb | aaBb | aB |
| aabb | aabb | ab |
What is a Dihybrid Cross?
A dihybrid cross is a breeding experiment that tracks two different traits simultaneously. While a simple monohybrid cross looks at one gene (like tall vs. short plants), a dihybrid cross examines how two independent genes get passed down together — like tracking both plant height and flower color at the same time.
🌱 Think of it this way: instead of asking "will the baby have brown eyes?", you're asking "will the baby have brown eyes AND curly hair?" — two questions, one calculation.
This approach was pioneered by Gregor Mendel in the 1860s when he crossed pea plants that differed in two traits (seed color and seed shape). His experiments revealed that genes for different traits typically sort independently during reproduction — what we now call the Law of Independent Assortment.
When each parent can produce 4 different gamete combinations, you need a 4×4 grid (16 squares) to show every possible offspring. That's what makes dihybrid crosses more complex — and why this calculator saves you serious time! For simpler single-trait problems, check out our Punnett Square Calculator.
How to Use This Calculator (Quick Start)
Just pick the genotype for each parent's two traits, and the calculator instantly generates the 4×4 Punnett square with all probabilities.
Select Mother's Trait A genotype
Choose AA (homozygous dominant), Aa (heterozygous), or aa (homozygous recessive) for the first trait.
Select Mother's Trait B genotype
Same options: BB, Bb, or bb for the second trait.
Repeat for Father
Select the father's genotypes for both Trait A and Trait B.
Read Your Results
The calculator instantly displays the 4×4 Punnett square and calculates probabilities for all 9 possible genotypes. Color-coding helps you quickly identify phenotype groups.
Step-by-Step Example: Hair Traits
Let's work through a real example: predicting whether a child will have curly or straight hair, and whether it will be dark or light colored.
The scenario:
- Mother: Curly blonde hair (heterozygous for curl: Aa, homozygous recessive for color: bb)
- Father: Straight blonde hair (homozygous recessive for both: aa and bb)
Our allele key:
Trait A (Hair Texture):
- • A = Curly (dominant)
- • a = Straight (recessive)
Trait B (Hair Color):
- • B = Dark (dominant)
- • b = Light/blonde (recessive)
Possible gametes for each parent:
Mother (Aabb)
Ab, ab
(2 unique gamete types)
Father (aabb)
ab
(only 1 gamete type possible)
🎯 Result: 50% of children will be Aabb (curly blonde hair), and 50% will be aabb (straight blonde hair). No dark-haired children are possible since neither parent carries a B allele!
The Classic 9:3:3:1 Phenotypic Ratio
When you cross two parents that are both heterozygous for both traits (AaBb × AaBb), you get the famous 9:3:3:1 ratio. This is the "classic" dihybrid cross result that Mendel discovered.
How to Calculate the Genotypic Ratio
If the calculator shows percentages like 6.25%, 12.5%, 25%, divide each by the smallest number to get simple integer ratios:
Percentages:
6.25 : 12.5 : 6.25 : 12.5 : 25 : 12.5 : 6.25 : 12.5 : 6.25
÷ 6.25
1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1
This is your genotypic ratio in simplest form
The 9:3:3:1 ratio only works when genes assort independently (are on different chromosomes) and show complete dominance. Linked genes or incomplete dominance will produce different ratios!
Real-World Examples & Use Cases
Agriculture & Crop Breeding
Breeders predict offspring traits like disease resistance + high yield, or drought tolerance + flavor quality in crops.
Dog & Cat Breeding
Calculate probabilities for coat color combinations, pattern types, or physical traits in planned litters.
Genetic Counseling
Help families understand inheritance risks when multiple genetic conditions run in the family.
Biology Education
Students learning Mendelian genetics can verify their manual Punnett square calculations and visualize inheritance patterns.
Research Planning
Scientists design breeding experiments and calculate expected ratios for model organisms like fruit flies or mice.
Understanding Your Own Traits
Curious about your family genetics? Explore how traits like eye color and earlobes might have been inherited. Try our Allele Frequency Calculator too!
Tips & Best Practices
Before using the calculator, make sure you know which allele is dominant (capital letter) and which is recessive (lowercase). Getting this wrong will flip your results!
Common mistakes to avoid:
- •Confusing genotype (genetic makeup: AaBb) with phenotype (observable trait: tall with brown eyes)
- •Forgetting that heterozygous parents (Aa or Bb) can produce offspring with the recessive phenotype
- •Assuming all traits follow simple Mendelian inheritance (many don't!)
- •Mixing up which parent is which when reading the Punnett square
🧠 Pro tip: If you're getting unexpected ratios in real breeding experiments, consider that genes might be linked (on the same chromosome) or showing incomplete dominance.
Understanding Genotype vs Phenotype
🧬 Genotype
The actual genetic code — the combination of alleles present in the DNA. Examples: AABB, AaBb, aabb
Think of it as the "recipe" in your genes.
👁️ Phenotype
What you can actually observe — the physical expression of the genotype. Examples: tall plant, brown eyes, curly hair
Think of it as the "finished dish" that results from the recipe.
Key terminology:
- Homozygous: Both alleles are the same (AA or aa)
- Heterozygous: The two alleles are different (Aa)
- Dominant: The allele that shows in the phenotype when present (usually capital letter)
- Recessive: The allele that only shows when two copies are present (usually lowercase)
Frequently Asked Questions
What's the difference between a monohybrid and dihybrid cross?
A monohybrid cross tracks one gene using a 2×2 Punnett square (4 outcomes). A dihybrid cross tracks two genes simultaneously using a 4×4 square (16 outcomes). Need the simpler version? Try our Punnett Square Calculator.
Why is the Punnett square 4×4 for two traits?
When a parent is heterozygous for both traits (AaBb), they can produce up to 4 different gamete combinations: AB, Ab, aB, and ab. With both parents potentially producing 4 gamete types each, you need 4×4 = 16 squares to show every possible combination.
What does "homozygous" vs "heterozygous" mean?
Homozygous means both alleles are identical (like AA or aa). Heterozygous means the two alleles are different (like Aa). Homozygous parents can only pass on one type of allele, while heterozygous parents can pass either version.
What's the probability of inheriting two recessive traits?
It depends entirely on the parents' genotypes! If both parents are heterozygous for both traits (AaBb × AaBb), there's a 1/16 (6.25%) chance of aabb offspring. But if both parents are homozygous recessive (aabb × aabb), it's 100%.
Can I use this for three or more traits?
The math scales up, but the Punnett square gets unwieldy fast! A trihybrid cross needs an 8×8 grid (64 squares). For multiple traits, most geneticists use probability multiplication or software instead of drawing out massive grids.
Why don't my real breeding results match the expected ratios?
Several possibilities: small sample sizes show more random variation, the genes might be linked (on the same chromosome), there could be incomplete dominance, or environmental factors might affect phenotype expression. The calculator shows theoretical probabilities — real life has more variables!
How do I read the phenotype from a genotype?
With complete dominance, any genotype containing at least one dominant allele shows the dominant phenotype. So AA, Aa, and aA all show the "A" phenotype. Only aa shows the recessive phenotype. The same logic applies to B/b.
Can I share my calculation with someone?
Yes! Use the Share button to generate a link that saves your exact parent genotype selections. Anyone clicking that link will see the same Punnett square and results you're looking at.
Limitations & Sources
- •This calculator assumes complete dominance and independent assortment — classic Mendelian genetics.
- •Real inheritance often involves linked genes, incomplete dominance, codominance, or epistasis — none of which are modeled here.
- •Probabilities are theoretical. Small sample sizes in real breeding may show different observed ratios due to chance.
- •This tool is for educational purposes — not a substitute for professional genetic counseling or veterinary/agricultural advice.
References & Further Reading
- •Nature Scitable: Gregor Mendel and the Principles of Inheritance
- •Khan Academy: Law of Independent Assortment
These external links are provided for deeper learning. Our calculator implements the classical Mendelian model.
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