Mendel selected pea plants because they could undergo continuous self-pollination, resulting in true-breeding lines that showed stable trait inheritance and expression for several generations. Mendel had access to 14 true-breeding pea plant varieties as pairs which were similar except for one character with contrasting traits.

The garden pea had characters manifested as two opposing traits such as tall or dwarf plants, yellow or green seeds, and smooth or wrinkled seeds. This allowed Mendel to set up a basic framework of rules governing inheritance.

Pea plants also permitted artificial pollination/cross-pollination experiments. The large sampling size gave greater credibility to the collected data, and inferences could be confirmed from experiments on successive generations of test plants.