Gregor Mendel
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Gregor Mendel works with his experimental organism, garden peas. As an Austrian monk, Mendel developed his theory of inheritance several decades before the behavior of chromosomes was observed in the microscope and their significance understood in the 1860s. Mendel chose to work with peas because they are available in many varieties. Biology states “The science of genetics provides explanations about not only the stability of inheritance but also the variations that are observed between generations and organisms” (p.182).
The use of peas gave Mendel strict control over which plants mated with which. The sex organs of a pea plant are in its flowers, and each pea flower has both male and female organs–stamen and carpel. In nature, the plants usually self-fertilize: Pollen grains released from the stamens land on the carpel of the same flower, and sperm from the pollen fertilize ova in the carpel. To achieve cross-pollination, Mendel removed the immature stamens of a plant before they produced pollen and then dusted pollen from another plant onto the emasculated flowers. Each resulting zygote then developed into a plant embryo encased in a seed. Whether ensuring self-pollination or executing artificial cross-pollination, Mendel could always be sure for the parentage of new seeds.
Mendel also made sure he started his experiments with varieties that were true-breeding, which means that when the plants self-pollinate, all their offspring are of the same variety. In a typical breeding experiment, Mendel would cross-pollinate two contrasting, true-breeding pea varieties. For example, a plant with purple flowers is true-breeding if the seeds produced by self-pollination all give rise to plants that also have purple flowers. Mendel usually followed traits for at least these three generations: the P, F1, and F2 generations.
If the blending model of inheritance were correct the F1 hybrids from a cross between purple-flowered and white-flowered pea plants would have pale purple flowers, intermediate between the two varieties of the P generation. Mendel reasoned that the heritable factor for white flowers did not disappear in the F1 plants, but only the purple flower factor was affecting flower color in these hybrids. In Mendels terminology, purple flower is a dominant trait and white flower is a recessive trait. The occurrence of white-flowered plants in the F2 generation was evidence that the heritable factor causing that recessive trait had not been diluted in any way by coexisting with the purple-flower factor in the F1 hybrids.
Mendel is known as the father of genetics even though he did not know about it while he was alive. Mendel use pea flowers because they were easy to manipulate their genetics. His experiment really explained the way human genetics are. Mendel did not know anything about DNA but he was able to figure out everything there is to know about genetics.