Dihybrid Cross Calculator
Calculate genetic probabilities for two traits using 4×4 Punnett squares with genotype and phenotype ratios
Dihybrid Cross Setup
Mother's Genotype (♀)
First genetic trait (e.g., hair texture)
Second genetic trait (e.g., hair color)
Father's Genotype (♂)
First genetic trait (e.g., hair texture)
Second genetic trait (e.g., hair color)
Dihybrid Cross Results
Genotype Probabilities
Phenotype Probabilities
🎯 Classic 9:3:3:1 phenotypic ratio detected! This is the expected result for AaBb × AaBb crosses.
Cross: AaBb (♀) × AaBb (♂)
Mother's gametes: AB, Ab, aB, ab
Father's gametes: AB, Ab, aB, ab
Total possible offspring combinations: 16
Interpretation Guide
A, B: Dominant alleles (usually expressed in phenotype)
a, b: Recessive alleles (expressed only when homozygous)
Genotype: The genetic makeup (e.g., AaBb)
Phenotype: The observable traits (e.g., AB = both dominant traits visible)
✅ 9:3:3:1 ratio indicates independent assortment of genes
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 |
How to read: Each cell shows the genotype of offspring from combining the corresponding gametes.
Pink headers show mother's gametes, blue headers show father's gametes.
Example: Hair Traits Inheritance
Scenario
Trait 1 (Hair Texture): A = Curly (dominant), a = Straight (recessive)
Trait 2 (Hair Color): B = Dark (dominant), b = Light (recessive)
Parents: Both parents are AaBb (curly dark hair, carriers)
Results
9/16 (56.25%): A_B_ - Curly, dark hair
3/16 (18.75%): A_bb - Curly, light hair
3/16 (18.75%): aaB_ - Straight, dark hair
1/16 (6.25%): aabb - Straight, light hair
Interpretation
• Classic 9:3:3:1 phenotypic ratio
• Most offspring have at least one dominant trait
• Only 6.25% have both recessive traits
• Demonstrates independent assortment of genes
Common Dihybrid Ratios
AaBb × AaBb
9:3:3:1 phenotypic ratio
Classic Mendelian inheritance
AaBb × aabb
1:1:1:1 phenotypic ratio
Testcross pattern
AABB × aabb
100% AaBb
F1 generation uniform
Genetic Terms
Dominant Allele
Expressed when present
Recessive Allele
Only expressed when homozygous
Heterozygous
Two different alleles
Homozygous
Two identical alleles
Understanding Dihybrid Crosses
What is a Dihybrid Cross?
A dihybrid cross examines the inheritance of two different traits simultaneously. It involves organisms that are heterozygous for two traits, resulting in a 4×4 Punnett square with 16 possible offspring combinations.
Key Principles
- •Each parent produces four types of gametes
- •16 possible offspring combinations
- •Classic AaBb × AaBb gives 9:3:3:1 ratio
- •Demonstrates independent assortment
Mendel's Second Law
Law of Independent Assortment
Genes for different traits are inherited independently
- 9/16: Both traits dominant (A_B_)
- 3/16: First dominant, second recessive (A_bb)
- 3/16: First recessive, second dominant (aaB_)
- 1/16: Both traits recessive (aabb)
Note: This ratio only applies when traits assort independently and show complete dominance.
Step-by-Step Process
1. Identify Genotypes
Determine the genotype of both parents for both traits
2. Form Gametes
Each parent produces 4 types of gametes combining alleles from both traits
3. Create Punnett Square
Make a 4×4 grid and fill in all 16 possible offspring combinations
4. Calculate Ratios
Count genotypes and phenotypes to determine probability ratios
Real-World Applications
Plant Breeding
- • Seed color and shape in peas
- • Flower color and plant height
- • Disease resistance and yield traits
- • Fruit size and sweetness
Animal Genetics
- • Coat color and pattern
- • Eye color and hair texture
- • Blood type and disease susceptibility
- • Behavioral and physical traits