Punnett Square Calculator
Calculate genotype and phenotype ratios from monohybrid or dihybrid crosses. Find probabilities of offspring genotypes using Punnett square analysis for dominant and recessive traits.
🧬 Genetics📐 Offspring ratios from parental cross🧬 Biology
Parent 1 genotype
Parent 2 genotype
Cross type
Please enter valid values.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Punnett Square Calculator | — | Offspring ratios from parental cross | probability |
Step-by-Step Examples
Example 1
Monohybrid Aa x Aa
Heterozygous x heterozygous cross for one trait.
- Gametes of Aa: A and a
- Cross: AA, Aa, aA, aa
- Genotype ratio: 1 AA : 2 Aa : 1 aa
- Phenotype ratio: 3 dominant : 1 recessive
✓ Genotypes: 1:2:1, Phenotypes: 3:1
Example 2
Carrier x Normal
Aa (carrier) x AA (normal). What are offspring risks?
- Gametes: Parent1 gives A or a; Parent2 gives only A
- Offspring: AA (50%) and Aa (50%)
- No aa offspring possible
✓ 50% normal AA, 50% carrier Aa; 0% affected
Example 3
Dihybrid AaBb x AaBb
Standard dihybrid cross for two independent traits.
- Each parent makes 4 gamete types: AB, Ab, aB, ab
- 4x4 Punnett square gives 16 combinations
- Phenotype ratio: 9 A_B_ : 3 A_bb : 3 aaB_ : 1 aabb
✓ 9:3:3:1 phenotype ratio (independent assortment)
Real-World Applications
Genetic Counseling
Calculate risk of inheriting recessive diseases (cystic fibrosis, sickle cell) from carrier parents.
Education
Fundamental teaching tool for Mendelian genetics in biology courses.
Plant Breeding
Predict offspring ratios in crop improvement programs for desired trait combinations.
Animal Breeding
Dog and livestock breeders use Punnett squares to predict coat color and other trait probabilities.
Common Mistakes to Avoid
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Upper case = dominant allele
Convention: A = dominant (expressed), a = recessive (only expressed in aa). BB and Bb both show dominant phenotype.
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Independent assortment for dihybrid
Dihybrid 9:3:3:1 ratio assumes genes are on different chromosomes (or far apart on same chromosome).
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Each square cell is equally probable
Each cell in the Punnett square has a 1/4 (monohybrid) or 1/16 (dihybrid) probability.
Frequently Asked Questions
What is a Punnett square? ▾
A grid showing all possible allele combinations from two parents. Rows = one parent gametes, columns = other parent gametes. Each cell = one possible offspring genotype.
What is the 3:1 phenotype ratio? ▾
From Aa x Aa: 3 show dominant phenotype (AA + Aa) : 1 shows recessive (aa). Classic Mendelian ratio for monohybrid cross of heterozygotes.
What is incomplete dominance? ▾
Heterozygote (Rr) shows intermediate phenotype between RR and rr. Example: red flower (RR) x white flower (rr) = pink flower (Rr). Ratio: 1 red : 2 pink : 1 white.
How does linkage affect dihybrid ratios? ▾
If genes are linked (on same chromosome), they do not assort independently. Ratio deviates from 9:3:3:1. Recombination frequency determines how much they deviate.
What is epistasis? ▾
One gene masks the expression of another. Modifies expected Mendelian ratios: 9:7, 9:3:4, 12:3:1, or 15:1 depending on epistasis type.