Question:

Given below are two statements : 

Statement I: Phenylketonuria is an example of Pleiotropy 
Statement II: Affected individuals lack an enzyme which converts pheylalanine into tyrosine 

In the light of the above statements, choose the most appropriate answer from the options given below : 
 

Updated On: May 14, 2024

  • Both Statement I and Statement II are correct

  • Both Statement I and Statement II are incorrect

  • Statement I is correct but Statement II is incorrect

  • Statement I is incorrect but Statement II is correct

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The Correct Option is A

Solution and Explanation

Both Statement I and Statement II are correct. 

Statement I: Phenylketonuria (PKU) is an example of Pleiotropy. Pleiotropy refers to a single gene influencing multiple phenotypic traits. In the case of PKU, a mutation in the gene responsible for producing the enzyme phenylalanine hydroxylase (PAH) leads to various phenotypic effects beyond the inability to metabolize phenylalanine. 

Statement II: Affected individuals lack an enzyme that converts phenylalanine into tyrosine. This statement accurately describes the underlying cause of PKU. Due to the absence or dysfunction of phenylalanine hydroxylase, individuals with PKU cannot convert phenylalanine into tyrosine, leading to an accumulation of phenylalanine in the body. 

Therefore, both Statement I and Statement II are correct.

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Concepts Used:

Principles of Inheritance and Variation - Mutation

A Mutation is a change in the sequence of our DNA base pairs caused by numerous environmental stimuli such as UV light or mistakes during DNA replication. Germline mutations take place in the eggs and sperm and can be passed onto offspring, whereas somatic mutations take place in body cells and are not passed on.

Types of Mutations

There are three types of mutations, which are as follows:

Silent mutation

It refers to any change in DNA sequence that has no effect on the amino acid sequence in a protein or the functions that a protein performs. There is no phenotypic indication that a mutation has occurred.

Nonsense mutation

When there is a change in the sequence of base pairs due to a point mutation, that results in a stop codon. This leads to a protein that is either shortened or non-functional.

Missense mutation

A missense mutation occurs when a point mutation causes a change in the codon, which then codes for another amino acid.

The mutation is caused by the following factors:

Internal Causes

When DNA copies incorrectly, the majority of mutations occur. Evolution occurs as a result of all of these mutations. DNA makes a copy of itself during cell division. When a copy of DNA isn't flawless, it's called a mutation since it differs somewhat from the original DNA.

External Causes

When certain chemicals or radiations are used to break down DNA, it causes the DNA to break down. The thymine dimers are broken by UV radiation, resulting in altered DNA.