0.41 Mendel’s experiments enbio

Johann Gregor Mendel (1822–1884) ( [link] ) was a lifelong learner, teacher, scientist, and man of faith. In 1865, Mendel presented the results of his experiments with nearly 30,000 pea plants to the local natural history society. He demonstrated that traits are transmitted faithfully from parents to offspring in specific patterns.

Mendel’s work went virtually unnoticed by the scientific community, which incorrectly believed that the process of inheritance involved a blending of parental traits that produced an intermediate physical appearance in offspring. This hypothetical process appeared to be correct because of what we know now as continuous variation. Continuous variation is the range of small differences we see among individuals in a characteristic like human height. It does appear that offspring are a “blend” of their parents’ traits when we look at characteristics that exhibit continuous variation. Mendel worked instead with traits that show discontinuous variation    . Discontinuous variation is the variation seen among individuals when each individual shows one of two—or a very few—easily distinguishable traits, such as violet or white flowers.

Mendel’s crosses

Mendel’s seminal work was accomplished using the garden pea, Pisum sativum , to study inheritance. “True-breeding,” pea plants are plants that always produce offspring that look like the parent. Large quantities of garden peas could be cultivated simultaneously, allowing Mendel to conclude that his results did not come about simply by chance.

Mendel performed hybridizations , which involve mating two true-breeding individuals that have different traits. In the pea, which is naturally self-pollinating, this is done by manually transferring pollen from the anther of a mature pea plant of one variety to the stigma of a separate mature pea plant of the second variety.

Plants used in first-generation crosses were called P    , or parental generation, plants ( [link] ). Mendel collected the seeds produced by the P plants that resulted from each cross and grew them the following season. These offspring were called the F ₁    , or the first filial (filial = daughter or son), generation. Once Mendel examined the characteristics in the F ₁ generation of plants, he allowed them to self-fertilize naturally. He then collected and grew the seeds from the F ₁ plants to produce the F ₂    , or second filial, generation. Mendel’s experiments extended beyond the F ₂ generation to the F ₃ generation, F ₄ generation, and so on, but it was the ratio of characteristics in the P, F ₁ , and F ₂ generations that were the most intriguing and became the basis of Mendel’s postulates.

Garden pea characteristics revealed the basics of heredity

In his 1865 publication, Mendel reported the results of his crosses involving seven different characteristics, each with two contrasting traits. A trait    is defined as a variation in the physical appearance of a heritable characteristic. The characteristics included plant height, seed texture, seed color, flower color, pea-pod size, pea-pod color, and flower position. For the characteristic of flower color, for example, the two contrasting traits were white versus violet. To fully examine each characteristic, Mendel generated large numbers of F ₁ and F ₂ plants and reported results from thousands of F ₂ plants.