Each trait is influenced by both paternal and maternal DNA. For each trait, there are two versions in the offspring. These two traits may be different or may be identical, depending upon the parentage. Thus, some traits may be inherited but not expressed. The hidden trait is called recessive and the expressed trait is called dominant.
For example: When Mendel crossed the tall pea plants of F1 generation, he found that tall and dwarf plants were obtained in F2 generation. He noted that the dwarf trait of the parent pea plant that disappeared in the F1 generation progeny re-appeared in F2 generation. Mendel concluded that the dwarfness traits of parent pea plant were not lost. They were suppressed in the F1 generation to re-appear in the F2 generation. In this way, Mendel called expressed traits of tallness as dominant or suppressed traits of dwarfness as recessive.