Monohybrid Cross Calculator
Predict offspring probabilities for a single Mendelian trait. Customize allele symbols and phenotype descriptions to generate a custom 2x2 Punnett square.
Trait details & Parental Genotypes
Customize dominant and recessive phenotypes, then select parent genotypes.
Mendelian 2×2 Grid
| A | a | |
|---|---|---|
| A | AA | Aa |
| a | Aa | aa |
Trait Probabilities
Genotype Ratio
Phenotype Ratio
Expert Tip
In complete Mendelian dominance, heterozygous individuals ($Aa$) display the dominant phenotype. Thus, a cross between two heterozygotes results in a 3:1 phenotypic ratio.
Methodology & Equations
Law of Segregation
Gregor Mendel's First Law (Law of Segregation) states that during gamete formation, the two alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.
Mendelian Ratios
For a monohybrid cross of two heterozygotes ($Aa \times Aa$):
- **Genotypic Ratio:** 1 AA : 2 Aa : 1 aa (1:2:1)
- **Phenotypic Ratio:** 3 Dominant : 1 Recessive (3:1)
How to Predict a Monohybrid Cross: Step-by-Step
Below is a step-by-step example crossing a heterozygous purple flower (Aa) with a homozygous white flower (aa):
Determine Parent Alleles
Parent 1 (Aa) contributes 'A' or 'a' gametes. Parent 2 (aa) contributes only 'a' gametes.
Fill the 2x2 Grid
Place Parent 1 gametes (A, a) along the columns and Parent 2 gametes (a, a) along the rows.
Top row cells: Aa, aa.
Bottom row cells: Aa, aa.
Summarize Ratios
Count genotypes: 2/4 Aa (50%), 2/4 aa (50%).
Translate to phenotypes: 50% Purple flower (dominant Aa) and 50% White flower (recessive aa).
Related Calculators
View All Biology Tools →Punnett Square Calculator
Generate custom 2x2 Punnett squares and calculate genotype probabilities.
Dihybrid Cross Calculator
Generate a 4x4 Punnett square for a two-trait dihybrid cross.
Incomplete Dominance Calculator
Analyze intermediate blended phenotypes of offspring.