Genetics & Punnett Square Calculator

Generate Punnett squares for genetic crosses. Supports monohybrid (one gene), dihybrid (two genes), incomplete dominance, and sex-linked inheritance. See color-coded genotypes, phenotype ratios, and step-by-step analysis.

Punnett Square2×2

Controls

Cross Type

Presets

Parent 1

Parent 2

Dominant Phenotype

Recessive Phenotype

Cross Summary

\text{Aa} \times \text{Aa}

Genotype Ratios

Genotype	Count	Fraction	Probability
aa	1	$\frac{1}{4}$	25.0%
Aa	2	$\frac{2}{4}$	50.0%
AA	1	$\frac{1}{4}$	25.0%

Genotype ratio: 1:2:1

Phenotype Ratios

Round

3/4 (75.0%)

Wrinkled

1/4 (25.0%)

Phenotype ratio: 3:1

Step-by-Step

Step 1 Determine parent gametes

\text{Parent 1 gametes: } A, a \quad \text{Parent 2 gametes: } A, a

Step 2 Fill the Punnett square by combining each pair of gametes

Step 3 Count genotypes and determine phenotypes

\text{Genotype ratio } = 1:2:1 \quad \text{Phenotype ratio } = 3:1

Step 4 Calculate probabilities

P(\text{Round}) = \frac{3}{4} = 75.0\%

P(\text{Wrinkled}) = \frac{1}{4} = 25.0\%

Reference Guide

Mendelian Genetics

Gregor Mendel discovered that traits are passed from parents to offspring through discrete units called genes. Each organism carries two copies (alleles) of each gene, one from each parent.

Dominant alleles (uppercase, like A) mask the effect of recessive alleles (lowercase, like a). A heterozygous individual (Aa) shows the dominant phenotype.

Law of Segregation

\text{Aa} \rightarrow \frac{1}{2}A + \frac{1}{2}a

Punnett Squares

A Punnett square is a grid that predicts the genotypes of offspring from a genetic cross. Parent gametes line the top and left sides, and each cell shows one possible offspring genotype.

Monohybrid cross (Aa x Aa)

\text{Genotype ratio: } 1\,AA : 2\,Aa : 1\,aa

Phenotype ratio

3 \text{ dominant} : 1 \text{ recessive}

Incomplete Dominance and Codominance

Not all traits follow simple dominance. In incomplete dominance, the heterozygote shows a blended phenotype between the two homozygous forms.

Snapdragon flowers

RR \text{ (red)} \times R'R' \text{ (white)} \rightarrow RR' \text{ (pink)}

Phenotype ratio (Aa x Aa)

1 \text{ red} : 2 \text{ pink} : 1 \text{ white}

In codominance, both alleles are fully expressed (e.g., AB blood type where both A and B antigens appear).

Sex-Linked Inheritance

Genes located on the X chromosome follow X-linked inheritance patterns. Males (XY) have only one X, so a single recessive allele will be expressed.

Color blindness (carrier mother)

X^A X^a \times X^A Y

Females can be carriers (heterozygous) without showing the trait. Males are either affected or unaffected because they carry only one X allele.

Result

\text{50\% sons affected, 50\% daughters carriers}