Punnett Square Calculator

Instantly generate crosses, determine parent gametes, and calculate exact phenotypic ratios. Supports standard Mendelian monohybrid (Aa × Aa) and dihybrid (AaBb × aabb) crosses.

Parent 1 Genotype

Parent 2 Genotype

Please enter valid genotypes (e.g., 2 letters like ‘Aa’ or 4 letters like ‘AaBb’ for both parents).

Aa × Aa AaBb × AaBb AAbb × aaBB Aa × aa (Test Cross)

Calculating independent assortment…

1 Determine Parent Gametes

2 Punnett Square Generation

Combining alleles from intersecting rows and columns.

3 Probability & Ratios

Genotypic Ratio: 1:2:1:2:4:2:1:2:1

Phenotypic Ratio: 9:3:3:1

9/16 Dominant A, Dominant B (56.25%)
3/16 Dominant A, Recessive b (18.75%)
3/16 Recessive a, Dominant B (18.75%)
1/16 Recessive a, Recessive b (6.25%)

Get the Exact Probabilities

See the full statistical breakdown of phenotypes and genotypes for your homework.

🔒 Reveal Step-by-Step Answer

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How to Solve Mendelian Genetics Problems

A Punnett square is a visual, grid-based tool used by biologists to predict the probability of an offspring possessing a particular genotype. Developed by Reginald Punnett, this simple tabular method is the cornerstone of classical Mendelian genetics. Whether you are in high school biology or preparing for the MCAT, understanding how to construct and read these squares is absolutely essential.

Monohybrid vs. Dihybrid Crosses

Our free Punnett square calculator is programmed to handle the two most common types of Mendelian crosses:

Monohybrid Cross (e.g., Aa × Aa): Tracks the inheritance of a single trait. The parents are typically heterozygous. This cross results in a 2×2 grid (4 possible offspring combinations) and classically yields a 3:1 phenotypic ratio and a 1:2:1 genotypic ratio.
Dihybrid Cross (e.g., AaBb × AaBb): Tracks the inheritance of two independent traits simultaneously (following Mendel’s Law of Independent Assortment). This requires finding all possible gamete combinations using the FOIL method, resulting in a 4×4 grid (16 combinations).

Understanding Phenotypic Ratios

When solving genetics homework, professors often ask for the phenotypic ratio. Here is a quick reference table for standard Mendelian crosses involving complete dominance:

Cross Type	Parent Genotypes	Standard Phenotypic Ratio
Monohybrid (Heterozygous)	Aa × Aa	3:1 (75% Dominant, 25% Recessive)
Monohybrid (Test Cross)	Aa × aa	1:1 (50% Dominant, 50% Recessive)
Dihybrid (Heterozygous)	AaBb × AaBb	9:3:3:1
Dihybrid (Test Cross)	AaBb × aabb	1:1:1:1

The FOIL Method for Dihybrid Gametes

The biggest mistake students make with dihybrid crosses is incorrectly determining the parent gametes. You must use the FOIL method (First, Outer, Inner, Last). For a parent with the genotype AaBb:

First: A and B = AB
Outer: A and b = Ab
Inner: a and B = aB
Last: a and b = ab

Our dihybrid cross solver online automates this step entirely, showing you the exact gametes before constructing the grid.

Frequently Asked Questions

How do you solve a dihybrid cross?

First, find the gamete combinations for each parent using the FOIL method (First, Outer, Inner, Last). Then, create a 4×4 grid. Place one parent’s gametes along the top and the other’s along the left side. Combine the alleles from the intersecting rows and columns to find the offspring genotypes.

What is the phenotypic ratio of a heterozygous dihybrid cross?

A cross between two individuals heterozygous for two traits (e.g., AaBb × AaBb) always results in a 9:3:3:1 phenotypic ratio under standard Mendelian inheritance with independent assortment and complete dominance.

Can this solver handle non-Mendelian genetics?

This specific calculator is optimized for standard Mendelian genetics involving complete dominance. However, you can use our text-based AI explainer on the homepage to ask complex questions about incomplete dominance, codominance, sex-linked traits, and epistasis.