Which of the following show Pleiotropism?

The correct answer is Option (2) → Phenylketonuria

Option (2) Phenylketonuria — Correct. One gene mutation in phenylketonuria causes mental retardation and less hair and skin pigment.

NCERT Extract:
Pleiotropy – “We have so far seen the effect of a gene on a single phenotype or trait. There are however instances where a single gene can exhibit multiple phenotypic expression. Such a gene is called a pleiotropic gene. The underlying mechanism of pleiotropy in most cases is the effect of a gene on metabolic pathways which contribute towards different phenotypes. An example of this is the disease phenylketonuria, which occurs in humans. The disease is caused by mutation in the gene that codes for the enzyme phenyl alanine hydroxylase (single gene mutation).”