Mendel called the trait that appeared unchanged in first-generation hybrids dominant. He contrasted it with the recessive trait, which was not visible in the F1 plants but could reappear in their descendants.
In his pea experiments, Mendel crossed true-breeding plants with different versions of a characteristic, such as purple and white flowers or round and wrinkled seeds. When the parental plants differed, the F1 hybrids generally displayed only one parental form. Mendel described that expressed form as dominant.
When F1 hybrids were allowed to self-pollinate, the hidden alternative returned in the F2 generation. For a typical single-trait cross, the visible phenotypes followed an approximate 3:1 dominant-to-recessive ratio, while the underlying genotypes followed a 1:2:1 pattern.
“Dominant” does not mean stronger, better, or more common in nature. It describes how one allele’s effect is expressed relative to another allele in a particular genetic context. Mendel introduced the paired terms dominant and recessive in his account of hybridization, published in 1866. Later geneticists supplied concepts such as genes, alleles, and genotypes.