Mendel found edible pea (pisum sativum) as the best material for his
hybridization experiments. The pea plant has
various contrasting
characters among its different varities. The flowers of the pea
plant are also constructed so that the pollens of a flower normally
fall on the stigma of the same flower and thus effects self pollinaion
or self fertilization. He prevented self fertilization by
removing the stamens from the flower buds. He cross pollinated
two desired pea plants differing in a particular pair of contrasting
characters. For getting the exact results in the breeding
experiments, it was necessary for Mendel to rear genetically pure
variety of pea plants for single character. He adopted the self
fertilization technique for this. In order to get pure characters
for tallness, he self fertilized a tall pea plant for many generations
till the resulted
offsprings always produced only tall plants.
Likewise, he got genetically pure varieties of dwarf pea plants.
He cross pollinated these two varieties of pea plants. When he
made observations of the offsprings of the first
generation, he found
only tall plants. He allowed self pollination in the offsprings
of the first generation and made further observations on the offsprings
of the second generation. He noted both tall and dwarf offsprings
in the second generation. This showed him that the character of
dwarfness dissappeared in the first generation but again reappeared in
the second generation. Further, the tall and dwarf plants of the
second generation were always in the ratio of 3:1. He self
pollinated the dwarf offsprings of the second generation and found only
dwarf plants of third generation. But when he self
pollinated the tall plants of the second generation, he found that
one-third (1/3) tall plants yield only tall plants in the third
generation, while the rest two- thirds(2/3) tall plants yield tall and
dwarf plants in the ratio 3:1. On the basis of these experiments, he
formulated three laws:1. Law of dominance.2. Law of
segregation.3. Law of independent assortment.