Why did Mendel choose the pea? First, peas have many easily distinguishable features. For example, pea flowers are either purple or white. Mendel studied seven individual traits: flower color, flower position, seed color, seed shape, pod color, pod shape, and plant height. Second, peas are easy to grow, so Mendel could collect data from thousands of plants, making his statistical analysis more accurate. Finally, Mendel could manipulate their reproduction to control which plants mated with which.

Pea plants usually fertilize themselves, as pollen released from the male reproductive organ, the stamen, lands on the female reproductive organ, the carpel. Mendel performed cross-pollination, or fertilization between plants, by removing the stamens from a plant, and brushing pollen from the stamens of another plant onto the carpel with a paintbrush. Mendel used only true-breeding plant strains in his experiments. A true-breeding strain is composed of identical individuals that always produce offspring with identical characteristics when cross-pollinated.

Before starting his experiments, Mendel cross-pollinated plants for several generations to make sure they were true-breeding. An X between parents indicates a cross, and an arrow connects parents with their offspring. Mendel studied each of the seven traits one at a time for many generations. Let’s use his study of flower color to understand his experimental method.

Mendel’s first set of experiments involved a monohybrid cross, which is a cross between two individuals that differ in only one trait. For example, he crossed true-breeding white-flowered plants with true-breeding purple-flowered plants. The original generation of any crossing scheme is called the parental, or P, generation. The offspring of the parental cross belong to the first filial, or F1, generation. Filial means relating to offspring. After he obtained the F1 plants, he allowed them to self-pollinate. The offspring of each F1 plant made up the F2, or second filial, generation. To make sure his calculations were statistically accurate, Mendel counted large numbers of offspring in each generation

Now let’s learn about Mendel’s laws!

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