Gregor Mendel, also known as "The Father of Genetics" was an Austrian monk that made a huge discovery about genetics because of his mini garden full of pea plants.
What made Mendel come to this experiment was because of the different phenotype or traits of the pea plants. Some were tall and some were short. Some plants either had purple or white flowers. Gregor observed each trait and saw how they were passed down to the offspring plants.
After breeding plants, Gregor Mendel learned that there are dominant traits that show in the plant, and that there are recessive traits that hide behind the dominant. He also found out that if short and tall plants bred, they would create a hybrid, which has both alleles from each parent. The hybrid could have the dominant trait, and also the recessive allele.
When Mendel was breeding plants, he discovered that when there was a tall and short plant, they made four tall plants. But when a hybrid mixed with a hybrid one out of four of the pea plants were short. Mendel was very confused, and kept breeding. After a while, Mendel finally discovered how to tell how many plants were going to be tall and short. He figured this out using the punnett square. The punnett square is a little chart that shows which trait your "creation" is going to get. It is a rough estimate, but it is better that nothing.
Sadly, Gregor Mendel's work was not discovered in his lifetime. Then, scientists in the 1900's proved his work to be right. Without Mendel, we would have never figured out this mystery.