Mendel’s experiment on pea plant

Mendel’s experiment

Step 1: Selection of true breeding varieties:

Mendel selected the true breeding varieties for his experiments as parental generation (P generation). True breeding varieties are the varieties that give rise to same trait for number of successive generations.
Mendel allowed several generations of pea plant to self-pollinate and verified that each variety was genetically pure (homozygous for each of the traits that he chose to study) by growing the plants for two generations and confirming that all offspring were same as their parents.

Step 2: Hybridization of true breeding varieties:

Hybridization is a process when two individuals having contrasting character are crossed.
Mendel conducted crosses between different true breeding plants to obtain hybrid plants. Theese hybrids were named as F1 (first filial) generation or F1 plants. When Mendel examined the F1 plants, he found that expressed only one of the phenotypes present in the parental generation.
He also conducted reciprocal cross but result was same in F1 generation.

Step 3: Self-pollination of F1 plants:

When two individuals having same genotype are crossed, are called selfing or self-pollination.
Mendel planted F1 seeds and cultivated the plants and allowed them to self-pollinate producing a second generation or F2 plants in 3:1 ratio of parental triats.

Mendel’s result appeared in the following pattern:

For any character the F1 generation derived from crosses between different varieties showed only one of the trait and never the other. The form of trait expressed was also called as dominant and the one that remained hidden as recessive.
It did not matter which parent variety provided the pollen and which the ova: but the results of both were always the same.
The trait which was disappeared or been hidden in the F1 generation reappeared in the F2 generation but only in frequency one quarter that of the total number. It means that in F2 generation, both the parental forms are reappeared in the ratio of 3:1 of which 50% were recombinants or hybrids.
The ratio of the dominant from to recessive form was always 3:1 that is the dominant form was three times the number of the recessive form.

In an artificial cross between two pure breeding plants (stock or parent), one tall plant and the other dwarf plant were cross pollinated.
The seeds obtained from cross pollination are cultivated to developed plants which represented the first filial generation (F1).

In F1 generation, all offspring were tall plant. They were not intermediate between the tall and dwarf as might be expected.
Similar results were obtained regardless of whether pollen grains or ova taken from dwarf plants or tall plant.
As Mendel noticed, one of the contrasting character is dominant and other is recessive. Tall character expressed among all F1 generation so, it is represented as dominant character whereas dwarf character remains unexpressed in F1 generation and is represented as recessive character.
Mendel allowed the hybrid plants of first generation to self-pollination.
The seeds obtained from F1 plants were planted which developed into plants of second filial generation (F2).
In F2 generation both tall and dwarf characters appeared in the ratio of approximately 3 tall to one dwarf (3:1).
Mendel look 1064 F2 hybrid and grew them into plants. Among F2 plants, 787 were tall and 277 short (dwarf), i.e. in the ratio of 2.84 tall to 1 dwarf or on allowing for experimental error due to chance, it comes to 3:1.
Plants of F2 generation were allowed self-pollination and the F3 generation was raised.
Result of F3 generation:
- All F2 dwarf plants (1/4) on self-pollination produced seeds which developed into dwarf plants
- Out of 3/4 Tall plant in F2, 1/3 produced only talls whereas the remaining 2/3 produced both tall and dwarf plants in 3:1 ratio as in F1 generation.