Statements (a), (b), (c), and (d) are missing from the input text, making it impossible to select the correct option. However, based on the textbook, Pleiotropism is defined as the phenomenon where a single gene exhibits multiple phenotypic expressions. A classic example provided is Phenylketonuria, a genetic disorder caused by a mutation in the gene coding for the enzyme phenylalanine hydroxylase (single gene). This manifests as mental retardation and a reduction in hair and skin pigmentation (multiple phenotypes) . Other examples include Starch synthesis in pea seeds and Sickle cell anemia.