The genes are sorted into separate gametes, ensuring variation. The most important principle of Mendel's Law of Independent Assortment is that the emergence of one trait will not effect the emergence of another. Mendel's findings allowed other scientists to simplify the emergence of traits to mathematical probability. A large portion of Mendel's spectacular findings can be traced to his proper usage of the scientific method. His choice of peas as a subject for his experiments is extraordinarily lucky.
Peas have a relatively simple genetic structure.
Also, Mendel could always be in control of the plants' breeding. When Mendel wanted to cross-pollinate a pea plant he needed only to remove the immature stamen of the plant. In this way he was always exactly sure of his plants' parents. Mendel made certain to start his experiments only with true breeding plants. He also only measured absolute characteristics such as color, shape, and position of the offspring.