Mutation is seen in –
**Core Concept**
The question is testing the understanding of genetic disorders and the role of mutations in causing them. A mutation is a change in the DNA sequence of an individual, which can result in various diseases.
**Why the Correct Answer is Right**
The correct answer involves a specific type of mutation that affects the structure and function of a protein. The mutation in question is a **point mutation**, which is a change in a single nucleotide base in the DNA sequence. This type of mutation can result in a change in the amino acid sequence of a protein, leading to a **gain-of-function** or **loss-of-function** effect. In the context of the correct answer, the point mutation affects the **Huntingtin gene**, leading to Huntington's disease, a fatal genetic disorder characterized by progressive damage to the brain.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify a type of mutation. While mutations can be categorized into various types, including point mutations, insertions, deletions, and duplications, the question is asking for a specific type of mutation.
* **Option B:** This option is incorrect because it does not mention a specific gene or protein affected by the mutation.
* **Option C:** This option is incorrect because it does not describe a type of mutation that affects the structure and function of a protein.
**Clinical Pearl / High-Yield Fact**
Huntington's disease is an autosomal dominant disorder, meaning that a single copy of the mutated gene is sufficient to cause the disease. The age of onset of the disease is inversely correlated with the number of CAG repeats in the Huntingtin gene.
**Correct Answer:** B.