Gregor Mendel's first notable experiment involved selecting from a large population of pea plants a few that differed from the majority in a particular trait. He found a few short-stemmed pea plants within a large population of long stemmed pea plants, a few with yellow seeds among the normal plants with green seeds, a few with wrinkled seeds among those with mostly round seeds, and so on. In all, Mendel studied seven contrasting phenotypic traits.
Mendel next crossed plants exhibiting contrasting traits. For example, he crossed tall plants with short plants, plants with green seeds with plants with yellow seeds, and so on. He then waited for the progeny (offspring or resulting generation) of each cross to develop, and observed their various phenotypes. The progeny plants then went on to produce a second generation of progeny, and the phenotypic traits of these plants were observed. Mendel went on to follow inheritance patterns of the progeny for several more generations.
In his first relevant experiment, Mendel used pea plants in which the parent generation were the offspring of genetically different parents (hybrids). The parents then, were hybrids for a particular trait. Through a process of crossing (and reciprocal crossing) both spherical seed strains and dented seed strains, this produced an F1 generation of spherical seed strain. The dented seed strain did not appear, so Mendel went on to test 253 plants from the above F1 generation of spherical seed strain. Then, by using a monohybrid cross which involved allowing the spherical seeds to self-pollinate, an F2 generation was produced. Mendel found that of 7,324 seeds of the F2 generation, 5,474 were spherical and 1,850 were dented. This meant that the dented seeds reappeared in the F2 generation, after having disappeared for the F1 generation.
The results of Mendel's first experiment showed that there was a distinct difference between the two types of seed strains (spherical and dented), as well as the two types of generations (F1 and F2). Mendel was able to see that the spherical seed trait tended to be overwhelmingly "dominant" (in appearance) over the dented seed trait. Since the dented seed trait only appeared in a 1:3 ratio to the spherical seed trait, it was called "recessive."
When Mendel crossed plants differing in one trait, the F1 generation always provided one of the two possible traits, the dominant trait. The important discovery was that the following generation, F2, showed the reappearance of the recessive trait. Mendel was able to show a constant ratio of approximately 3:1, where the dominant trait expressed in the F1 generation was expressed roughly three times as much as the recessive trait when in the F2 generation.
The MendelWeb is a great link to information on Gregor Mendel. If you are proficient in German, than you can especially enjoy reading Mendel's documentation of his work.
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