Crossing of two genetically different individuals is called hybridisationExample:

i. Crossing of homozygous tall (U) and dwarf (if) pisum plants.

ii. Crossing of homozygous black (BB) and white (bb) Guinea pigs.

Hibridisation experiments were conducted even before Mendel by German scientist Kolreuter on tobacco plant. But kolreuter failed to propose.

principles of inheritance because he took all the characters in a plant as a single unit. Why Mendel succeeded in proposing principles of inheritance?.
1. His success mainly depends upon the selection of pea plants. . They sharply differ in few characters.
2. The plants are annuals and produce many generations within a short span.
3. The plants are self pollinated. The flowers facilitated cross pollination also. The cross pollination is carried out by removing anthers from the flowers of female parent. by emasculation.
4. He studied the inheritance of one character at a time in the begining and later two or more.
5. Mendel continued his experiments upto ‘F3’ generation (F = Filial or daughter generation)
6. He analysed the results statistically which enabled him to derive the numerical ratios.
7. “Selection of pure breeding strains as the starting material was important for his success”.
8. Mendel conducted experiments on seven characters or traits, each of which exists in two forms (dominant and reccessive)
10. ‘F’ generation
It is the filial generation produced due to hybridisation. In hybridisation experiment, first produced progeny is called ‘F1’ (1 - first ; f - filial) generation and second produced is called ‘F2’ (2 - second; F-filial) generation.
11. Hybrids
The first progeny (‘F1’ generation) produced due to hybridisation are called hybrids. These are always heterozygous.