Mendel studied several different traits of a pea plant. For example, some pea plants have purple flowers and others have white flowers. Pea plants can either self-fertilize or cross-fertilize. Crossing two plants is called hybridization. To start, however, Mendel needed plants that were true-breeding. This means that after generations of self-breeding, the pea plant expressed only one version of the trait. After many generations a purple flowered plant only produced plant never produced a white flowered plant.
