Punnett Square Calculator – Predict Genetic Cross Outcomes

Generate Punnett squares for monohybrid and dihybrid genetic crosses with our free calculator. Calculate genotype and phenotype ratios and probabilities instantly. Perfect for biology students, genetics courses, and science teachers.

Cross Type

Parent 1 Genotype

Allele 1

Allele 2

Parent 2 Genotype

Allele 1

Allele 2

Understanding Punnett Squares

A Punnett square predicts the probability of offspring genotypes from a genetic cross. You place parent alleles on the top and side, then fill in the boxes with possible combinations.

Key Terms

Allele: Different forms of a gene (e.g., A or a)
Genotype: Genetic makeup (e.g., AA, Aa, aa)
Phenotype: Physical trait expressed
Dominant: Allele that masks the recessive (capital letter)
Recessive: Allele only expressed when homozygous (lowercase)
Homozygous: Two identical alleles (AA or aa)
Heterozygous: Two different alleles (Aa)

Monohybrid Cross Example

Cross: Aa × Aa (both parents heterozygous)

Expected ratio: 1 AA : 2 Aa : 1 aa (25% : 50% : 25%)

Phenotype ratio (if A is dominant): 3 dominant : 1 recessive (75% : 25%)

Dihybrid Cross Example

Cross: AaBb × AaBb

Classic phenotype ratio: 9:3:3:1

9/16 show both dominant traits
3/16 show first dominant, second recessive
3/16 show first recessive, second dominant
1/16 show both recessive traits

Genotype Distribution

Enter values and calculate to see the chart

Common Genetic Crosses

Cross	Genotype Ratio	Phenotype Ratio
AA × aa	100% Aa	100% dominant
Aa × aa	1 Aa : 1 aa	1 dominant : 1 recessive
Aa × Aa	1 AA : 2 Aa : 1 aa	3 dominant : 1 recessive
AA × Aa	1 AA : 1 Aa	100% dominant

How to Use This Punnett Square Calculator

Select cross type

Choose monohybrid for single-trait inheritance or dihybrid for two-trait crosses involving two genes.

Enter parent genotypes

Input the alleles for each parent. Use capital letters for dominant traits and lowercase for recessive.

Generate and analyze results

Click Generate to see the Punnett square grid, genotype probabilities, and phenotype ratios for your cross.

Key Features of This Calculator

Monohybrid and Dihybrid Crosses

Supports both single-gene and two-gene inheritance patterns with accurate probability calculations

Visual Punnett Square Grid

See the actual 2x2 or 4x4 grid showing all possible offspring genotype combinations

Genotype Probability Chart

Pie chart visualization shows the distribution of genotypes at a glance

Reference Tables

Includes common genetic cross ratios and key terminology for learning

Mendelian Inheritance Patterns Reference

Parent Cross	Genotype Ratio	Phenotype Ratio	Example
Homozygous × Homozygous	100% heterozygous	100% dominant	TT × tt = all Tt
Heterozygous × Homozygous Recessive	1:1	1:1	Tt × tt
Heterozygous × Heterozygous	1:2:1	3:1	Tt × Tt
Dihybrid Cross	Various	9:3:3:1	TtRr × TtRr

Note: These ratios assume complete dominance and independent assortment.

Frequently Asked Questions

What is a Punnett square used for?

A Punnett square predicts the probability of offspring inheriting specific genetic traits. It shows all possible combinations of parental alleles and calculates the likelihood of each genotype and phenotype in the next generation.

What is the difference between genotype and phenotype?

Genotype is the genetic makeup (like BB, Bb, or bb). Phenotype is the physical trait you can observe (like brown eyes or blue eyes). Two organisms can have different genotypes but the same phenotype if one allele is dominant.

How do dihybrid crosses work?

Dihybrid crosses track two genes simultaneously. Each parent produces four types of gametes (AB, Ab, aB, ab), creating a 4x4 grid with 16 possible offspring. The classic ratio is 9:3:3:1 for two heterozygous parents.

What does capital vs lowercase mean?

Capital letters represent dominant alleles that express their trait even when paired with a different allele. Lowercase letters are recessive alleles that only show their trait when two copies are present (homozygous recessive).

Are Punnett squares always accurate?

Punnett squares show probabilities, not certainties. They assume independent assortment and complete dominance. Real inheritance can involve linked genes, incomplete dominance, codominance, and environmental factors that complicate predictions.

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