Punnett Square Calculator
Calculate genetic inheritance probabilities for single traits using 2×2 Punnett squares with genotype and phenotype ratios
Monohybrid Cross Setup
Mother's Genotype (♀)
Mother's genetic makeup for the trait
Possible Gametes:
Father's Genotype (♂)
Father's genetic makeup for the trait
Possible Gametes:
Punnett Square Results
Cross Pattern:
Classic Mendelian cross (3:1 phenotypic ratio)
Aa (♀) × Aa (♂)
Genotype Probabilities
Phenotype Probabilities
Interpretation Guide
A: Dominant allele (expressed when present)
a: Recessive allele (only expressed when homozygous)
Genotype: The genetic constitution (AA, Aa, or aa)
Phenotype: The observable characteristic (A or a phenotype)
Gametes: Reproductive cells carrying one allele each
2×2 Punnett Square
| ♂\♀ | A | a |
|---|---|---|
| A | AA | Aa |
| a | Aa | aa |
How to read: Each cell shows the genotype of offspring from combining the corresponding gametes.
Pink headers represent mother's gametes, blue headers represent father's gametes.
The four cells show all possible offspring genotypes with equal probability (25% each).
Example: Cystic Fibrosis Inheritance
Medical Scenario
Trait: Cystic Fibrosis (autosomal recessive disorder)
A: Normal allele (dominant)
a: Cystic fibrosis allele (recessive)
Parents: Both are carriers (Aa × Aa)
Results
25% (AA): Normal, not a carrier
50% (Aa): Normal, but carrier
25% (aa): Has cystic fibrosis
Phenotypic ratio: 3:1 (normal : affected)
Clinical Significance
• 25% chance of affected child
• 75% chance of healthy child
• 50% of healthy children will be carriers
• Important for genetic counseling
Common Genetic Crosses
Aa × Aa
3:1 phenotypic ratio
Classic Mendelian cross
AA × aa
100% Aa (F1 generation)
All heterozygous
Aa × aa
1:1 phenotypic ratio
Testcross
AA × AA
100% AA
All dominant
Genetic Definitions
Homozygous Dominant
Two dominant alleles
Heterozygous
One dominant, one recessive
Homozygous Recessive
Two recessive alleles
Mendelian Ratio
Classic dominant:recessive
Understanding Punnett Squares
What is a Punnett Square?
A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from a genetic cross. It was developed by British geneticist Reginald Punnett and is fundamental to understanding Mendelian inheritance.
Key Principles
- •Each parent contributes one allele per trait
- •Dominant alleles mask recessive alleles
- •Each offspring combination has equal probability
- •Results predict statistical expectations
Mendel's First Law
Law of Segregation
Each parent passes only one allele to offspring
- Dominant (A): Expressed when present
- Recessive (a): Only expressed when homozygous
- Heterozygous: Carriers of recessive traits
- Homozygous: Pure breeding for a trait
Note: Punnett squares assume simple dominance and independent assortment.
Step-by-Step Process
1. Determine Genotypes
Identify the genetic makeup of both parents
2. Find Gametes
Determine possible alleles each parent can contribute
3. Create Square
Make a 2×2 grid and combine alleles
4. Analyze Results
Calculate genotype and phenotype probabilities
Applications in Medicine and Breeding
Medical Genetics
- • Genetic counseling for hereditary diseases
- • Risk assessment for genetic disorders
- • Understanding carrier status
- • Predicting disease susceptibility
Agriculture & Breeding
- • Crop improvement programs
- • Animal breeding strategies
- • Trait selection and enhancement
- • Maintaining genetic diversity