Final answer:
The concept of dominance is related to the expression of one allele over another, where the dominant allele masks the effects of the recessive allele in a heterozygous organism.
Step-by-step explanation:
The concept of dominance (Mendel's Third Law) is associated with the expression of one allele over another. Gregor Mendel's law of dominance states that in a heterozygote, the dominant trait will conceal the presence of another trait for the same characteristic. When Mendel crossed purple flowered-plants with white flowered-plants, all the offspring had purple flowers, indicating the purple flower trait was dominant over the white flower trait. This means that in the presence of the dominant allele, the recessive allele becomes latent, and its effects are not observed in the organism's phenotype. The recessive allele will only be expressed when an organism carries two copies of this recessive allele.