Given below are two statements :
Statement I : Phenylketonuria is an example of pleiotropy .
Statement II : Affected individual lacks an enzyme that converts phenylalanine into tyrosine.
In the light of the above statements, choose the most appropriate answer from the options given below :
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both statement I and statement II are correct .
Statement I : Phenylketonuria is an example of pleiotropy . — Correct. In pleiotropy a single gene affects many traits. In phenylketonuria the one faulty gene causes mental retardation and less hair and skin pigmentation.
Statement II : Affected individual lacks an enzyme that converts phenylalanine into tyrosine. — Correct. The gene for the enzyme phenylalanine hydroxylase is mutated, so phenylalanine piles up and is changed into harmful products.
NCERT Extract:
Pleiotropy – “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). This manifests itself through phenotypic expression characterised by mental retardation and a reduction in hair and skin pigmentation.”