Final answer:
The demonstration of genes expressed refers to an organism's phenotype, which is the set of observable traits. Phenotype can be affected by environment and gene expression levels, showcasing traits that might not directly reveal underlying genotypes. Gene expression changes as per the requirements of the organism, which impacts the phenotype.
Step-by-step explanation:
The demonstration of the genes expressed, rather than what genes actually code for, refers to an organism's phenotype. Phenotype consists of the observable traits expressed by an organism resulting from gene expression. In contrast, an organism's genotype is its underlying genetic makeup, including alleles that are not necessarily expressed.
Mendel's hybridization experiments with plants demonstrated the concept of phenotype versus genotype. When true-breeding parent plants with distinct pod colors were cross-fertilized, the F1 generation displayed a phenotype identical to one of the parents, despite possessing a different genotype. This illustrates that the physical manifestation, or phenotype, does not always unveil the full genetic composition, or genotype, of an organism.
Gene expression changes based on necessity, much like how personal expressions change with emotions. Different proteins are synthesized as needed, contributing to the phenotype depending on the cellular circumstance and environmental factors.