A Punnett square is a visual representation of a cross. The genotypes of the parents are denoted along the top and the side of the grid. The possible genotypes of the offspring are obtained by combinig the different alleles in the grid.

The Punnett square below shows an example of a cross between a heterozygous father and a homozygous dominant mother.

A punnett square depicting the genotypes of the possible offspring of a father with genotype capital r lowercase r, and a mother with genotype capital r capital r. The punnet square contains two columns and two rows. The columns are labelled with the father’s genotype, so column 1 has a capital r and column two has a lowercase r. The rows are labelled with the mother’s genotype, so row 1 and row 2 are both labeled with capital r. The table’s contents are as follows: column 1, row 1: capital r capital r. Column 2, row 1: capital r lowercase r. column 1, row 2: capital r capital r. column 2, row 2: capital r, lowercase r.