What did Gregory Mendel use to test genetic crossovers?

The story behind the answer

Peas. Gregor Mendel, an Austrian monk, bred pea plants (Pisum sativum) with contrasting traits—such as round vs. wrinkled seeds, yellow vs. green peas, and tall vs. short stems—by carefully cross-pollinating them. Peas were ideal because they grow quickly, produce many offspring, have clear, binary traits, and can self- or cross-fertilize, letting Mendel control parentage precisely.

By counting thousands of offspring, he discovered predictable ratios (like 3:1 and 9:3:3:1) and formulated the laws of segregation and independent assortment, the foundations of genetics. Memory tip: P for Peas, P for Principles of inheritance—and Punnett squares. Although Mendel didn’t know about DNA or chromosomes, later science showed his patterns reflect meiosis and chromosomal behavior.