**Question:** A mutation that results in premature termination of incorporation of amino acid into a peptide chain is a

A. nonsense mutation
B. splice mutation
C. frameshift mutation
D. missense mutation

**Correct Answer:** A. nonsense mutation

**Core Concept:**
A mutation is a change in the DNA sequence that can lead to variations in proteins' structure, function, or stability. These mutations can be classified into different types based on their effects on the genetic code and protein synthesis.

**Why the Correct Answer is Right:**
A nonsense mutation is a type of genetic variation that occurs when a premature stop codon is introduced into the mRNA molecule during transcription. This premature stop codon disrupts the reading frame of the mRNA, leading to the termination of the amino acid synthesis before the completion of the normal protein sequence. As a result, the resulting protein is truncated and may lose its normal function or become nonfunctional.

**Why Each Wrong Option is Incorrect:**

A. Splice mutation (B): This type of mutation occurs at the site of intron-exon junctions, affecting the splicing process of pre-mRNA. It does not involve the premature termination of amino acid incorporation into the peptide chain.

B. Frameshift mutation (C): This type of mutation alters the reading frame of the mRNA sequence, leading to a change in the amino acid sequence of the resulting protein. Frameshift mutations do not result in premature termination of amino acid incorporation into the peptide chain.

D. Missense mutation (D): This type of mutation involves a change in a single nucleotide, resulting in a change in a single amino acid residue within the protein sequence. Missense mutations do not result in premature termination of amino acid incorporation into the peptide chain.

**Clinical Pearl:**
Understanding the different types of genetic mutations is crucial for medical professionals, as they play a role in diagnosing, treating, and counseling patients with genetic disorders. Nonsense mutations can be detected through molecular genetic testing, such as DNA sequencing, and may be treated with small molecules or antisense oligonucleotides to restore protein function.

**Core Concept:** Molecular genetics, genetic mutations, and their effects on protein synthesis.

**Clinical Application:** Appreciating the distinction between different types of genetic mutations helps medical professionals in diagnosing, treating, and counseling patients with genetic disorders. Nonsense mutations can be detected through molecular genetic testing, such as DNA sequencing. Treatments for nonsense mutations include small molecules or antisense oligonucleotides that can potentially restore protein function.