Punnett Square Calculator
Type any two parent genotypes and get the full Punnett square with genotype and phenotype ratios — monohybrid, dihybrid, or trihybrid.
Try Moustra freeHow to use the Punnett square calculator
- Enter Parent 1 genotype — type a genotype string such as
AaBborAa. Each letter represents one allele; uppercase is dominant, lowercase is recessive. Every locus needs exactly two alleles (one pair of letters). - Enter Parent 2 genotype — use the same gene letters as Parent 1 in the same order. Both parents must have identical loci for the cross to be valid, though each can be homozygous (AA) or heterozygous (Aa).
- Read the Punnett square — the grid updates instantly. Each cell shows the offspring genotype at the intersection of the two parent gametes. Scroll right for large dihybrid or trihybrid grids.
- Check the distribution tables — genotype and phenotype counts, fractions, and percentages are listed below the grid. The reduced phenotype ratio (e.g. 9:3:3:1) appears at the bottom of the phenotype table.
- Share or export — copy the shareable URL to send exact inputs to a colleague, or download a CSV of the distribution data for your records.
Understanding genotype vs phenotype ratios
The genotype ratio tells you how often each exact combination of alleles appears among offspring. For a dihybrid cross of two AaBb parents, nine distinct genotypes are possible (AABB, AABb, AAbb, AaBB, AaBb, Aabb, aaBB, aaBb, aabb), and each appears a predictable number of times across the 16-cell grid.
The phenotype ratio groups genotypes by observable expression. Because dominance masks the recessive allele, AaBb and AABB both produce the same phenotype (A_ B_). The classic dihybrid result — 9:3:3:1 — means 9 offspring show both dominant traits, 3 show only trait A dominant, 3 show only trait B dominant, and 1 shows both recessive. Understanding this distinction is essential for interpreting colony screening results when you cannot always sequence every animal.
In practice, Mendelian ratios are theoretical expectations for large numbers of offspring. Small litters may deviate substantially from predicted ratios by chance. Tracking actual genotype outcomes across many litters — as Moustra does — lets you confirm your cross is behaving as expected and flag deviations that might indicate linkage or other effects.
Frequently Asked Questions
What is a Punnett square?
A Punnett square is a diagram used to predict the possible genotypes of offspring from a cross between two parents. Invented by geneticist Reginald Crundall Punnett, it arranges all possible gametes of each parent along the axes so every cell represents one possible offspring combination. It is the standard tool for visualizing Mendelian inheritance in genetics courses and laboratory colony management.
How do I read a Punnett square?
Each row of the grid corresponds to one gamete from Parent 1 (left header) and each column to one gamete from Parent 2 (top header). The cell at row i, column j is the offspring genotype formed by combining those two gametes. Count how many cells share the same genotype to get the genotype ratio; group cells by dominant/recessive expression to get the phenotype ratio.
What is the difference between a monohybrid, dihybrid, and trihybrid cross?
A monohybrid cross tracks one gene locus (e.g. Aa × Aa), producing a 2×2 grid with 4 cells. A dihybrid cross tracks two loci (e.g. AaBb × AaBb), producing a 4×4 grid with 16 cells and the classic 9:3:3:1 phenotype ratio. A trihybrid cross tracks three loci, producing an 8×8 grid with 64 cells. This calculator supports all three and any valid combination of heterozygous or homozygous parents.
How are the genotype and phenotype ratios calculated?
The calculator counts how many cells in the grid share each unique genotype (e.g. AaBb appears 4 times out of 16 → 25%). For phenotype ratios it groups genotypes by expression pattern: any locus with at least one uppercase (dominant) allele is phenotypically dominant for that trait. The ratio is then reduced to lowest integer terms (e.g. 9:3:3:1). The fraction column shows exact counts over total cells.
Can I use real gene symbols instead of A, B, C?
Yes — the calculator accepts any single-letter allele symbols as long as uppercase = dominant and lowercase = recessive. For example, 'BbRr × BbRr' works the same as 'AaBb × AaBb'. Each locus must appear exactly twice (two alleles) per parent. Multi-letter gene symbols (like 'Bmp4') are not yet supported — use the first letter as a proxy.
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