Punnett Square Maker: Build and Check One- and Two-Trait Crosses

Select one trait, then enter two parent genotypes, such as Aa and Aa. The maker places each parent's gametes on an axis and pairs them in four offspring cells. Read the genotype and phenotype ratios below the grid, or turn on practice mode to fill in the cells first.

Select two traits and enter two-gene genotypes, such as AaBb and AaBb. The tool lists four gametes per parent and combines them into sixteen cells. Inspect each cell, or practice filling them in yourself. The 9:3:3:1 phenotype ratio applies when both traits show complete dominance and assort independently.

A basic 2×2 or 4×4 square cannot reliably predict human eye or hair color. These traits involve many genes and other biological factors. This maker models one or two Mendelian traits under a chosen dominance rule, so use it to learn allele combinations and probabilities, not to forecast appearance.

It supports 2×2 grids for one-gene crosses and 4×4 grids for two-gene crosses. A one-gene heterozygote cross gives two gametes per parent, and two heterozygous genes give four per parent. Other genetic setups can create different dimensions, but this maker does not include a 3×3 mode.

The ABO system has three alleles in the population and its own dominance relationships, which a two-allele model cannot represent. The codominant setting groups a heterozygote as its own phenotype for classroom use only. For blood-type questions, use a dedicated ABO calculator with verified parental blood genotypes.

Turn on practice mode, type a genotype into each 2×2 or 4×4 offspring cell, then select Check my grid. The maker marks correct cells and cells to retry. Selected row and column gametes give you a hint. Reveal one cell or the full answer key when you need it, then export the grid.

The genotype ratio counts exact allele combinations, so an Aa × Aa cross gives 1 AA : 2 Aa : 1 aa. The phenotype ratio groups those combinations by the inheritance rule you select. With complete dominance, AA and Aa share the dominant category, so the same cross gives three dominant outcomes for every recessive one.