Gregor Mendel discovered this principle (also often called the law of dominance) in his classic studies of inheritance patterns. When genes of certain allelic pairs have contrasting effects on the same trait, only one can be expressed, while the other one will remain “masked.” The gene that is expressed is called the dominant allele; the one that is masked is the recessive allele. In order to understand this, geneticists use symbols to represent the genes—usually the dominant genes are represented by capital (italicized or not) letters, while the recessive genes are represented by lowercase (italicized or not) letters.

All tall offspring result in the above example.