**Question:** A mutation in the codon which causes a change in the coded amino acid, is known as

A. Mutation
B. Polymorphism
C. Insertion
D. Deletion

**Correct Answer:** .

**Core Concept:**
A codon is a group of three nucleotides in an mRNA molecule that specifies the identity of an amino acid during protein synthesis in cells. Mutations in these codons can lead to changes in the amino acid sequence of the translated protein, which can have significant effects on the protein's structure and function.

**Why the Correct Answer is Right:**
A mutation in the codon, specifically a change in the nucleotide sequence, leads to a change in the corresponding amino acid being encoded by that codon. This type of mutation is known as a "nonsense mutation" or "missense mutation." In a nonsense mutation, the change results in an early stop codon, leading to a truncated protein. In a missense mutation, the change results in a different amino acid being coded for.

**Why Each Wrong Option is Incorrect:**

A. Mutation (overall term for changes in DNA or RNA) is correct, but the specific type of mutation (either nonsense or missense) is what defines the change in the coded amino acid.
B. Polymorphism refers to genetic variations that are common and not necessarily causing a change in the coded amino acid.
C. Insertion and deletion mutations change the number of nucleotides in the codon but do not directly alter the coded amino acid.

**Clinical Pearl:**
Understanding the different types of mutations and their effects on protein structure and function is crucial for genetic counseling, diagnostics, and therapeutic approaches in genetic disorders. It is essential to recognize missense mutations in genetic testing and counseling, as they can lead to a vast array of clinical manifestations depending on the gene and protein involved.