Mendel used pea plants because of their ability to propagate in large numbers and because of the ease with which their reproduction can be manipulated. These benefits allowed him to breed purebred plants selectively with certain traits and observe how those traits changed over many generations.
Pea plants have both male and female reproductive organs and thus can self-pollinate or cross-pollinate with other plants. Mendel's experiments concluded that genetic traits observed in offspring occur without any blending of the traits given by the parents. He also found that certain traits are dominant over others and are likely to occur more frequently in subsequent generations.
Because of the dominance of certain traits, there exists the possibility that if a parent's trait does not appear in the offspring, it can recur in the following generation. Using pea plants, Mendel could observe the patterns of inheritance that occurred between two generations of plants per year.
As of 2014, geneticists use species that replicate much quicker; fruit flies are used because they reproduce within two weeks and the bacteria E. coli is also used because they reproduce within 5 hours. Mendel's experiments also disproved early theories of evolution and inheritance proposed by Jean-Baptiste Lamarck, but Mendel is not credited for this because his work remained unknown until long after Lamarck's theories were deemed improbable.