Punnett Square Calculator
Predict offspring genotypes and phenotypes
Select parent genotypes to calculate inheritance probabilities and visualize the genetic cross.
Studying genetics? Select parent genotypes to instantly predict offspring trait probabilities with this Punnett Square generator!
Parent Genotypes
Offspring Probabilities
Punnett Square
| ♂ \ ♀ | A | A |
|---|---|---|
| A | AA | AA |
| A | AA | AA |
💡 Analyzing 2 traits simultaneously? Explore a dihybrid cross Punnett Square calculator to work with 4 alleles.
Genotype to Phenotype
| Genotype | Phenotype |
|---|---|
| AA | A (dominant trait) |
| Aa | A (dominant trait) |
| aa | a (recessive trait) |
What is a Punnett Square?
A Punnett Square is a simple grid that helps you predict the genetic outcomes of a cross between two parents. Named after British geneticist Reginald Punnett, this visual tool has been helping students and scientists understand inheritance patterns for over a century.
🧩 Think of it like a multiplication table — but instead of numbers, you're combining alleles (gene variants) from mom and dad to see what combinations their kids might get.
For a single-gene trait (called a monohybrid cross), the Punnett Square is a 2×2 grid showing four possible offspring genotypes. Each cell represents a 25% chance outcome.
🎓 Students
Learning genetics in biology class? This is your go-to tool for homework and exams.
🔬 Researchers
Planning breeding experiments with model organisms? Predict outcomes before you start.
👨👩👧 Parents
Curious about genetic traits in your family? Understand inheritance risks.
How to Use This Calculator (Step-by-Step)
Using our Punnett Square calculator is straightforward. Here's a quick walkthrough:
Select the Mother's Genotype
Choose from AA (homozygous dominant), Aa (heterozygous), or aa (homozygous recessive).
Select the Father's Genotype
Same options: AA, Aa, or aa.
Read the Offspring Probabilities
The calculator instantly shows the percentage chance for each genotype (AA, Aa, aa).
View the Punnett Square Grid
See exactly how alleles combine in the visual 2×2 table.
Share Your Results
Use the share button to generate a link with your specific inputs — perfect for study groups or discussions!
Example: Both parents are heterozygous (Aa × Aa)
Result: 25% AA, 50% Aa, 25% aa → 75% dominant phenotype, 25% recessive phenotype
Real-World Examples
🏥 Example 1: Predicting Cystic Fibrosis Risk
Background: Cystic fibrosis (CF) is an autosomal recessive disorder. Both parents are healthy but have family histories of CF — meaning they might be carriers (Aa).
Inputs:
- • Mother's genotype: Aa (carrier)
- • Father's genotype: Aa (carrier)
Results:
- • 25% chance child has CF (aa)
- • 50% chance child is a carrier (Aa)
- • 25% chance child is completely unaffected (AA)
Application: This information helps families make informed decisions and prepares them for genetic counseling.
🌱 Example 2: Plant Breeding (Flower Color)
Background: A gardener wants to breed purple flowers. Purple (P) is dominant over white (p). They cross a purple heterozygous plant with a white plant.
Inputs:
- • Purple parent: Pp (heterozygous)
- • White parent: pp (homozygous recessive)
Results:
- • 50% purple flowers (Pp)
- • 50% white flowers (pp)
Application: The gardener knows to expect about half white offspring — and can select only the purple ones for the next generation.
🐕 Example 3: Dog Coat Color
Background: In some dog breeds, black coat (B) is dominant over brown (b). A breeder crosses two black dogs, both known to be carriers of the brown allele.
Inputs:
- • Dog 1: Bb
- • Dog 2: Bb
Results:
- • 75% black puppies (BB or Bb)
- • 25% brown puppies (bb)
Application: The breeder can predict litter composition and set realistic expectations for buyers.
After working out trait probabilities, you might want to explore our Allele Frequency Calculator to understand population-level genetics, or check the Biology Calculators section for more tools.
Genotype vs. Phenotype: What's the Difference?
These two terms are essential for understanding Punnett Squares — and they're often confused!
🧬 Genotype
The genetic code — the actual allele combination an organism carries (AA, Aa, or aa).
It's the "hidden blueprint" that may or may not be visible from the outside.
👁️ Phenotype
The observable trait — what you actually see (tall/short, blue eyes/brown eyes, etc.).
The physical expression of the genotype, influenced by dominance.
🎯 Key insight: Two organisms can have the same phenotype but different genotypes. Both AA and Aa show the dominant trait — you can't tell them apart just by looking!
| Genotype | Type | Phenotype |
|---|---|---|
| AA | Homozygous Dominant | Dominant trait (A) |
| Aa | Heterozygous | Dominant trait (A) |
| aa | Homozygous Recessive | Recessive trait (a) |
Calculating Ratios from Aa × Aa Cross:
- Genotypic ratio: AA : Aa : aa = 1 : 2 : 1
- Phenotypic ratio: Dominant : Recessive = 3 : 1
Mendelian Inheritance: The Foundation
Gregor Mendel, a 19th-century monk, discovered the fundamental laws of inheritance by studying pea plants — without any knowledge of DNA! His insights form the backbone of modern genetics.
⚖️ Law of Segregation
Each parent has two alleles for a trait, but only passes one to each offspring. The alleles separate (segregate) during reproduction.
🎲 Law of Independent Assortment
Genes for different traits are inherited independently of each other (assuming they're on different chromosomes).
👑 Law of Dominance
When two different alleles are present, the dominant one masks the recessive one in the phenotype.
🧪 Modern Exceptions
We now know some traits show codominance (both alleles expressed) or incomplete dominance (blended expression).
🩸 Blood type is a great example of codominance: A and B alleles are both dominant, so someone with both (AB genotype) expresses BOTH traits — that's why we have blood type AB!
Tips & Best Practices
Use consistent notation
Always use CAPITAL letters for dominant alleles and lowercase for recessive. Mixing them up leads to confusion!
Check trait eligibility
Punnett Squares work best for simple, single-gene traits. Complex traits (height, intelligence) involve multiple genes and environment.
Remember: probabilities, not guarantees
A 25% chance doesn't mean exactly 1 in 4 children will have that genotype — it's a probability for each individual birth.
Consider carrier status
Healthy parents can be carriers (Aa) of recessive diseases. Family history matters when predicting offspring risks.
Common mistakes to avoid
- ✗Using Punnett Squares for traits controlled by multiple genes (polygenic traits)
- ✗Forgetting that environmental factors can also influence phenotype
- ✗Assuming all traits follow simple dominant/recessive patterns
- ✗Mixing up genotypic and phenotypic ratios
Common Cross Patterns & Results
Here are the nine possible monohybrid crosses and their expected outcomes:
| Cross | AA | Aa | aa | Phenotype Ratio |
|---|---|---|---|---|
| AA × AA | 100% | 0% | 0% | 100% dominant |
| AA × Aa | 50% | 50% | 0% | 100% dominant |
| AA × aa | 0% | 100% | 0% | 100% dominant |
| Aa × Aa | 25% | 50% | 25% | 75% : 25% (3:1) |
| Aa × aa | 0% | 50% | 50% | 50% : 50% (1:1) |
| aa × aa | 0% | 0% | 100% | 100% recessive |
For two traits at once (like pea color AND shape), you'd need a dihybrid cross with a 4×4 grid and 16 possible outcomes. The classic ratio is 9:3:3:1 when both parents are double heterozygotes.
Frequently Asked Questions
What is the purpose of a Punnett Square?
A Punnett Square helps predict the probability of offspring inheriting specific genotypes and phenotypes. It's a visual tool for understanding Mendelian inheritance patterns, useful in education, genetic counseling, and breeding programs.
How do I know if a genotype is heterozygous or homozygous?
Homozygous means both alleles are identical (AA or aa). Heterozygous means the alleles are different (Aa). In real life, you'd determine this through genetic testing or by analyzing inheritance patterns across generations.
Can Punnett Squares predict human traits accurately?
For simple single-gene traits (like cystic fibrosis, sickle cell, or Huntington's disease), yes! However, most human traits (height, skin color, intelligence) are polygenic — controlled by many genes — and can't be predicted with simple Punnett Squares.
Why is Aa called heterozygous?
"Hetero" means different in Greek. A heterozygous individual has two different alleles for a gene. "Homo" means same — so homozygous individuals have two identical alleles (AA or aa).
What's a dihybrid cross?
A dihybrid cross examines two traits simultaneously using a 4×4 grid with 16 possible outcomes. It demonstrates the Law of Independent Assortment. When both parents are double heterozygotes (AaBb × AaBb), the phenotype ratio is 9:3:3:1.
What traits can I use a Punnett Square for?
Punnett Squares work best for traits that are: (1) controlled by a single gene, (2) inherited independently, and (3) not significantly affected by environmental factors. Good examples include blood type, certain genetic disorders, and simple flower colors.
What does 25% probability really mean?
It means each offspring has a 25% chance of having that genotype — like flipping a coin. Having four children doesn't guarantee you'll get exactly one of each outcome. Each birth is an independent event with its own probabilities.
Can I share my Punnett Square results?
Yes! Use the share button to generate a link that includes your selected genotypes. Perfect for study groups, comparing scenarios with classmates, or discussing with family members about genetic inheritance.
Limitations & Sources
Important Limitations
- •This calculator assumes simple Mendelian inheritance with complete dominance.
- •It does not account for codominance, incomplete dominance, or linked genes.
- •Most human traits are polygenic (controlled by multiple genes) and cannot be predicted this way.
- •Environmental factors can also influence phenotype expression.
- •Results are probabilities, not guarantees — actual outcomes may vary.
Medical Disclaimer
This calculator is for educational purposes only. For genetic counseling, carrier testing, or medical decisions about inherited conditions, please consult a qualified healthcare professional or certified genetic counselor.
External References & Further Reading
Links are provided for educational reference. This calculator's examples use simplified assumptions for clarity.
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