Gregor Mendel: Planting the Seeds of Genetics

The Famous Pea Experiment

Mendel’s results depended on a lot of peas—and a lot of patience

Prior to Mendel, naturalists and scientists tried to understand heredity by crossbreeding different varieties of plants or animals. Nevertheless, Mendel was the first to conduct broad, thorough, systematic, and sufficiently rigorous experiments to discern any universal laws governing inheritance.

Mendel began by identifying seven pairs of contrasting traits found among garden peas:

	Seed color (yellow or green)
	Seed shape (smooth or wrinkled)
	Pod color (yellow or green)
	Pod shape (inflated or pinched)
	Flower color (purple or white)
	Flower position (axial or terminal)
	Stem height (tall or short)

For two years, the scientist grew different varieties of peas to make sure that their offspring were always the same. Then be began breeding different varieties together to make hybrids. He brushed the pollen off yellow pea plants and put it on green pea plants, and did the same for plants with each of the seven pairs of traits. He then grew generation after generation of hybrids and tracked the inheritance of the traits.

Mendel noticed that some traits disappeared in the first generation of hybrids. He called these traits “recessive.” He called those that did appear “dominant.” In later generations the recessive traits reappeared—and in a mathematically predictable pattern. For example, later generations of plants had one green pea for every three yellow peas. The same ratio appeared for all seven pairs of traits.

Mendel grew an estimated 28,000 pea plants over eight years. In 1864 he published the results of his experiment.

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