A mutation in a single gene coding for the enzyme phenylalanine hydroxylase leads to a cascade of effects in an affected individual, including mental retardation, reduction in hair, and loss of skin pigmentation. This genetic phenomenon, where a single gene exhibits multiple phenotypic expressions, is known as:

Step-by-step solution

The condition described is Phenylketonuria, an inborn error of metabolism. It is caused by a mutation in the single gene that codes for the enzyme phenylalanine hydroxylase. When a single gene influences multiple, seemingly unrelated phenotypic traits (such as mental retardation, hair reduction, and skin pigmentation changes), the phenomenon is termed pleiotropy. Polygenic inheritance (Option 1) is incorrect as it involves multiple genes controlling a single trait. Multiple allelism (Option 2) refers to more than t