🟩 Punnett Square Calculator
Cross two parent genotypes and get the full Punnett square with genotype and phenotype ratios — monohybrid, dihybrid or trihybrid.
Uppercase = dominant, lowercase = recessive. Try Aa × Aa (monohybrid), AaBb × AaBb (dihybrid), or AaBbCc (trihybrid).
| A | a | |
|---|---|---|
| A | AA | Aa |
| a | Aa | aa |
Genotype ratio
1 : 2 : 1
- AA — 1/4 (25.0%)
- Aa — 2/4 (50.0%)
- aa — 1/4 (25.0%)
Phenotype ratio
3 : 1
- A — 3/4 (75.0%)
- aa — 1/4 (25.0%)
How the punnett square calculator works
Enter each parent’s genotype (e.g. Aa, AaBb). The tool enumerates every gamete for each parent, fills the grid with all offspring combinations, and tallies the genotype ratios (like 1:2:1) and phenotype ratios (like 3:1 or 9:3:3:1). Uppercase letters are dominant alleles, lowercase recessive; a genotype shows the dominant phenotype if it carries at least one dominant allele for that gene.
This is exactly the case where a deterministic tool beats asking a chatbot: language models routinely mis-fill larger grids and mis-count the ratios. Here every cell and tally is computed, not guessed.
Frequently asked questions
How do you make a Punnett square?
List each parent’s possible gametes along the top and side of a grid, then fill each cell by combining the row and column alleles. For a monohybrid Aa × Aa cross the offspring are 1 AA : 2 Aa : 1 aa — a 3:1 dominant-to-recessive phenotype ratio.
What is the ratio for a dihybrid cross?
A dihybrid cross of two heterozygotes (AaBb × AaBb) gives a 9:3:3:1 phenotype ratio across a 4×4 grid of 16 boxes. This tool produces the full grid and the exact tallies automatically.
What do uppercase and lowercase letters mean?
Uppercase is the dominant allele, lowercase the recessive. An organism shows the dominant trait if it has at least one dominant allele (AA or Aa), and the recessive trait only when both alleles are recessive (aa).
Can it do trihybrid crosses?
Yes — enter three-gene genotypes like AaBbCc and it builds the 8×8 grid (64 boxes) and tallies the genotype and phenotype ratios.
What is the difference between genotype and phenotype ratio?
The genotype ratio counts the exact allele combinations (e.g. 1 AA : 2 Aa : 1 aa). The phenotype ratio counts the observable traits (e.g. 3 dominant : 1 recessive), grouping genotypes that look the same.
Why use a tool instead of drawing it?
For monohybrid crosses drawing is easy, but dihybrid (16 boxes) and trihybrid (64 boxes) crosses are error-prone by hand and often filled in wrong by AI chatbots. A deterministic grid removes the mistakes.
Related biology & lab tools
From the blog
Hardy–Weinberg Equilibrium: Allele Frequencies, p²+2pq+q², and the χ² Test
Hardy–Weinberg predicts genotype frequencies from allele frequencies: p²+2pq+q²=1. Find p and q from genotype counts (p = (2·AA+Aa)/2N), compute expected counts, and test for equilibrium with a chi-square goodness-of-fit — with a worked example.
Punnett Squares: Monohybrid, Dihybrid, and Where the 9:3:3:1 Comes From
A monohybrid Aa × Aa cross gives 1:2:1 genotypes and a 3:1 phenotype ratio; a dihybrid AaBb × AaBb gives 9:3:3:1. How to fill the grid, read the ratios, and why larger crosses are so easy to get wrong by hand.