(I) Pleiotropic genes have multiple phenotypic effects
(II) Multiple alleles exhibit the same phenotypic expression
(III) Cystic fibrosis and phenylketonuria are examples of pleiotropism

The correct option is B Statement I and III are correct while statement II is incorrect
The phenomenon where the expression of a single gene has multiple phenotypic effects is called pleiotropy. Cystic fibrosis and phenylketonuria are examples of pleiotropism.

Phenylketonuria is an autosomal recessive disorder where homozygous recessive individuals lack an enzyme called phenylalanine hydroxylase which converts phenylalanine to tyrosine in the liver. The absence of this enzyme leads to the accumulation of phenylalanine in the body causing skin pigmentation, mental retardation, and loss of hair.

Cystic fibrosis is an autosomal recessive disorder where chloride ion channels dysfunction and leads to the production of thick mucus which plugs the tubes and tracts in the body.

Multiple alleles are the existence of more than two alternative forms of a gene; they are located on the same locus of the homologous chromosomes. The phenotypic expressions of the alleles are different. For eample: The ABO blood group is controlled by three alleles $I^A,I^B\mathrm{and}i.$