The principle of dominance is a fundamental concept in genetics, first introduced by Gregor Mendel through his experiments with pea plants. This principle states that in a pair of contrasting alleles, one allele can mask or suppress the expression of the other allele. The allele that is expressed is called the dominant allele, while the allele that is masked is called the recessive allele.
For example, in Mendel’s experiments, when he crossed a purebred tall pea plant with a purebred short pea plant, all the offspring were tall. This happened because the allele for tallness (T) is dominant over the allele for shortness (t). Even though the offspring had one allele for tallness and one for shortness, the dominant allele (T) masked the expression of the recessive allele (t), resulting in all tall plants.
In summary, the principle of dominance explains how certain traits are expressed over others in offspring, with the dominant allele determining the observable characteristics while the recessive allele remains hidden unless present in a homozygous recessive state.