Final answer:
The observable traits expressed by an organism are referred to as its phenotype, while its underlying genetic makeup is called its genotype.
Step-by-step explanation:
The observable traits expressed by an organism are referred to as its phenotype. An organism's underlying genetic makeup, consisting of both physically visible and non-expressed alleles, is called its genotype.
Mendel's hybridization experiments demonstrate the difference between phenotype and genotype. For example, when true-breeding plants in which one parent had yellow pods and one had green pods were cross-fertilized, all of the F₁ hybrid offspring had yellow pods. This means that although the hybrid offspring were phenotypically identical to the true-breeding parent with yellow pods, their genotypes were different.