How did Gregor Mendel develop the idea of dominant and recessive traits?

Gregor Mendel developed the concepts of dominant and recessive traits through systematic cross-pollination experiments with garden peas in his monastery garden.1

By crossing pure-breeding lines—such as plants with yellow seeds and those with green seeds—he observed that the first generation (F1) offspring consistently displayed only one of the parental traits (e.g., all yellow seeds). When these F1 individuals were self-pollinated, the hidden trait reappeared in the second generation (F2) in a consistent 3:1 ratio.1

Mendel deduced that each plant carried two discrete hereditary units (now known as alleles) for each character. He concluded that one allele could exert a greater influence than the other, masking the expression of the second trait. The trait that appeared in the F1 generation was deemed dominant, while the trait that remained hidden but could reappear in later generations was termed recessive. This mathematical approach allowed him to establish the foundational principles of genetics and Mendelian inheritance.1234