In the mid-1800's, Gregor Mendel was a monk in a monastery that grew peas for food. They had yellow peas and green peas.

One day Gregor Mendel crossed the yellow peas with the green peas, but only yellow peas grew. Later he allowed the new yellow peas to self-fertilize. (Remember, plants have both the pollen and the pistil, and they can fertilize themselves.)

This time Mendel got many yellow peas and a few green peas. This is a basic genetics experiment.