Sir Gregor Johann Mendel (1822 to 1884) was Austrian monk who used garden pea (Pisum sativum) for his experiments on plant breeding and published his results in 1865. However, his work was independently rediscovered in 1900, long after Mendel’s death, by Tschermak, Correns and DeVries. But since Mendel was the first to suggest principles underlying inheritance he is regarded as the founder or father of genetics.
Mendel designed his experiments in such a way that a pure tall variety of pea plants could be crossed to a pure dwarf variety. The anthers from flowers of tall plants were removed and their stigmas dusted with pollen from flowers of dwarf plants. The reverse experiment was also carried out, that is anthers of flowes borne on dwarf plants were removed and their stigmas were dusted by pollen from flowers of tall plants.
In the following spring, seeds from the new plants were collected and sown. Mendel found that all the plants of this generation called first filial generation or F1 grew to be tall plants. He allowed them to self pollinate. Again he collected the seeds. The following year, after the seeds had been sown, he found that three quarters of these plants were tall and the rest dwarf. He repeated the experiment several times and found that the ratio of tall to dwarf plants was 3:1.
In this way he tried to cross pea plants differing in seven such contrasting characters or traits. These were:
- red flowered and white flowered plants
- axillary flowered (flower arising in the axial of the leaf) and terminal flowered (flower arising at tip of stalk)
- yellow seeded versus green seeded
- round seeded versus wrinkled seeded
- green pod versus yellow pod
- plants with inflated pods versus those with constricted pod
- pure tall plants versus pure dwarf plants
Plants with these contrasting characters existed in varieties that were self pollinating so that generation after generation they expressed only one type of feature.
Crosses involving plants differing in the inheritance of one contrasting feature only are called monohybrid crosses. Mendel also tried crosses involving two contrasting features, such as tall and red flowered plants crossed with dwarf and white flowered plants. Such crosses are termed dihybrid crosses.