Punnett Square Calculator (Monohybrid)

A Punnett Square is a grid used in genetics to predict the possible gene combinations — and therefore inherited traits — that offspring can receive from two parents. Enter your Parent 1 Genotype, Parent 2 Genotype, dominant allele, and recessive allele into the Punnett Square Calculator to see the full 2×2 grid. Results include the Genotype Ratio, Phenotype Ratio, dominant and recessive phenotype probabilities, and the percentage of heterozygous offspring. Also try the find Rh Positive Probability with Rh Factor Inheritance Calculator.

Enter two alleles (e.g., Aa for heterozygous)

Enter two alleles (e.g., Aa for heterozygous)

Enter the dominant allele letter

Enter the recessive allele letter

Description of dominant trait expression

Description of recessive trait expression

Results

Genotype Ratio

--

Phenotype Ratio

--

Dominant Phenotype Probability

--

Recessive Phenotype Probability

--

Heterozygous Offspring

--

Results Table

What is a Punnett Square Calculator?

A Punnett Square Calculator is a genetic tool that predicts the probability of offspring inheriting specific traits from their parents. It creates a grid showing all possible genetic combinations from a cross between two parents. See also our Map Distance Calculator (centiMorgans).

How do I use this monohybrid Punnett square calculator?

Enter the genotypes of both parents using allele letters (e.g., Aa, AA, aa), specify the dominant and recessive alleles, and optionally add phenotype descriptions. The calculator will automatically generate the Punnett square and show ratios.

What's the difference between genotype and phenotype ratios?

Genotype ratio shows the proportion of different genetic combinations (like AA:Aa:aa = 1:2:1), while phenotype ratio shows the proportion of observable traits (like Purple:White = 3:1 when A is dominant over a).

How do I tell if a genotype is heterozygous or homozygous?

A heterozygous genotype has two different alleles (like Aa), while a homozygous genotype has two identical alleles (like AA or aa). Heterozygous individuals carry both dominant and recessive alleles. You might also find our calculate Chi-Square Goodness of Fit (Genetics) Chi-Square Value (χ²) useful.

What does a 3:1 ratio mean in genetics?

A 3:1 phenotype ratio typically results from crossing two heterozygous parents (Aa × Aa). It means 75% of offspring show the dominant trait and 25% show the recessive trait.

Can this calculator handle incomplete dominance?

This monohybrid calculator is designed for complete dominance patterns. For incomplete dominance or codominance, you would need specialized calculators that account for blended or co-expressed traits.

What is the purpose of a Punnett square in genetics?

Punnett squares help predict inheritance patterns, calculate the probability of genetic disorders, plan breeding programs, and understand how traits pass from parents to offspring in sexually reproducing organisms.