Final answer:
Mendel prevented self-pollination by removing anthers of pea flowers before maturation and controlled cross-pollination by manually transferring pollen from a different plant, enabling him to study inheritance.
Step-by-step explanation:
To prevent self-pollination and control cross-pollination in his experiments, Gregor Mendel used a meticulous technique. Since pea plants are naturally self-pollinating, Mendel had to ensure that he could produce hybrids by cross-pollination.
He first removed the flower's anthers before they matured, taking away the plant's ability to self-pollinate. Afterwards, he hand-pollinated these flowers using pollen from another plant of the desired variety. By doing so, he could conduct controlled experiments to observe the inheritance patterns of specific traits in the peas, eventually leading to his foundational laws of inheritance.