Gregor Mendel didn't specifically prevent his pea plants from self-pollinating to ensure that they didn't produce round seeds. Instead, he focused on cross-pollination to study the inheritance of traits. Here's how he did it:

* Preventing Self-Pollination: Pea plants naturally self-pollinate, meaning pollen from the same flower fertilizes the ovules. To prevent this, Mendel carefully removed the male reproductive parts (anthers) from the flowers of his plants.

* Cross-Pollination: He then transferred pollen from the anthers of a plant with one trait (e.g., round seeds) to the stigma of a plant with a different trait (e.g., wrinkled seeds). This ensured that the offspring would inherit genes from both parents, allowing him to observe how traits were passed down.

Mendel's experiments were groundbreaking because he meticulously controlled the breeding process. This allowed him to isolate and study the inheritance of specific traits, leading to the foundation of modern genetics.