He started his experiments by breeding plants that were pure for each trait. Parent plants that are pure (homozygous) always produce offspring with that trait. He obtained a total of 14 pure strains. One for each of seven pairs of contrasting traits. He cross pollinated the plants by hand. He crossed pure tall plants to pure short plants. Pure wrinkled seeded plants with pure smooth seeded plants, etc. When the plants seeded, he grew large numbers of these and recorded how many and what kinds of plants grew.

1. Mendel's first hypothesis was that inherited characteristics are controlled by factors that occur in pairs.

2. Mendel's second hypothesis stated that one factor (dominant) in a pair mask the other (recessive) preventing it from showing its affect.

4. The fourth hypothesis is that different factors are inherited separately (such as seed color does not have any connection with the height of a pea plant).
Mendel called the original parents P1 for parent generation and the offspring of the cross F1 for the first filial generation. He called the next cross F2 for second filial generation.
When Mendel crossed tall pea plants with the short pea plants of the P1 generation, all of the F1 plants were tall. The same thing happened with each of the seven traits, only one form of each characteristic appeared in the F1 plants.

To find out where the characteristic for short plants had went, he crossed the F1 plant to the F1 plant to get F2 plants, in which appeared the short plants again.

Not only did it reappear but with a certain predictable mathematical relationship, 1 short and 3 tall. The same relationship, also, showed up for all of the seven traits.