Punnett Squares

A Punnett square is a powerful tool named after the scientist Reginald C. Punnett. It shows the possible genetic combinations from a genetic cross.

To create a Punnett square, we start by identifying each parent's genetic makeup or genotype. Then, draw a square divided into four smaller boxes and label each parent's alleles—a gene's different forms—along the grid's top and side.

To fill the boxes, combine the alleles to show all the possible genetic outcomes of their offspring.

For example, consider a pair of rabbits. One parent has black fur, and the other has white fur.

If the black-furred parent carries one dominant allele for black fur and one recessive allele for white fur, and the white-furred parent has two recessive alleles for white fur, a Punnett square can show the possible outcomes.

There is a 50 percent chance of the offspring having black fur, inheriting one dominant and one recessive allele, and a 50 percent chance of having white fur, inheriting two recessive alleles.