Given below are two statements. One is labelled Assertion (A) and the other is labelled Reason (R).

Assertion (A) : The individual affected by phenylketonuria lacks an enzyme that converts phenyl alanine to tyrosine.

Reason (R) : In PKU affected individuals tyrosine accumulates in the brain. 

In light of the above statements, choose the correct answer from the options given below.

(A) is true but (R) is false.

Assertion (A) states that the individual affected by phenylketonuria (PKU) lacks an enzyme that converts phenylalanine to tyrosine, which is true. Phenylalanine hydroxylase (PAH) is the enzyme that converts phenylalanine to tyrosine, and individuals with PKU have a deficiency or complete absence of this enzyme.

Reason (R) states that in PKU-affected individuals, tyrosine accumulates in the brain, which is false. Because phenylalanine cannot be converted to tyrosine due to the enzyme deficiency, phenylalanine levels increase in the body. Excess phenylalanine is converted into other harmful substances, such as phenylpyruvate and phenylacetate, which can damage the brain. Meanwhile, since tyrosine cannot be synthesized from phenylalanine, tyrosine levels are reduced, leading to its deficiency.