Identify the statements which hold true for Phenylketonuria.
(A) Phenylketonuria is a sex linked disorder
(B) Phenylpyruvic acid is accumulated and converted to phenylalanine
(C) It is caused by mutation in a pleiotropic gene
(D)The affected individual lacks enzyme phenylalanine hydroxylase
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (C) and (D) only
(A) Phenylketonuria is a sex linked disorder — False. It is autosomal recessive.
(B) Phenylpyruvic acid is accumulated and converted to phenylalanine — False. It is the other way round: phenylalanine accumulates and is converted into phenylpyruvic acid.
(C) It is caused by mutation in a pleiotropic gene — True. One gene mutation gives several effects.
(D) The affected individual lacks enzyme phenylalanine hydroxylase — True.
NCERT Extract:
Mendelian Disorders – “… Phenylketonuria : This inborn error of metabolism is also inherited as the autosomal recessive trait. The affected individual lacks an enzyme that converts the amino acid phenylalanine into tyrosine. As a result of this phenylalanine is accumulated and converted into phenylpyruvic acid and other derivatives. Accumulation of these in brain results in mental retardation.”
Pleiotropy – “… 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).”