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Question #45811
The Question
Phenylketonuria (PKU) is an autosomal recessive inborn error of metabolism that classically illustrates the genetic principle of pleiotropy. Regarding the biochemical and genetic basis of its pleiotropic manifestations, which of the following statements is INCORRECT?
Options
- A.
The primary metabolic block occurs due to a defective gene failing to synthesize the enzyme phenylalanine hydroxylase.
- B.
Intellectual disability results from the accumulation of phenylalanine and its subsequent transamination into neurotoxic phenylpyruvic acid.
- C.
Hypopigmentation of the skin and hair occurs because the metabolic block prevents the formation of tyrosine, the primary precursor for melanin.
- D.
The pleiotropic nature of the mutation arises because the affected gene directly codes for multiple distinct enzymes required for both neural development and melanogenesis.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Phenylketonuria|Tyrosine_Metabolism|Mental_Retardation
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often misunderstand the mechanism of pleiotropy.
They confuse 'multiple phenotypic expressions' with the gene producing 'multiple distinct proteins'.
The trap in Option D exploits this by suggesting a single gene directly codes for multiple enzymes, violating the general 'one gene-one enzyme' concept applicable here, whereas true pleiotropy involves a single primary metabolic block causing a ripple effect across different physiological systems.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Principles of Inheritance and Variation - Class 12 |
| Concept | Pleiotropy Logic |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |