**Core Concept**
The nonsense mutation is a type of point mutation that occurs in a gene, resulting in a premature stop codon in the mRNA transcript. This type of mutation leads to a truncated or incomplete protein product, often causing loss of function or gain of a toxic protein.

**Why the Correct Answer is Right**
A nonsense mutation occurs when a point mutation changes a codon to one of the three stop codons (UAA, UAG, or UGA) in the mRNA transcript. This premature stop codon leads to the termination of protein synthesis, resulting in a truncated protein product. The mutation is called "nonsense" because it introduces a stop signal into the middle of the coding sequence, rather than at the end. This can lead to a loss of function of the protein, as the truncated protein may not be able to perform its normal function.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because nonsense mutations are not typically associated with frameshift mutations, which occur when a nucleotide is inserted or deleted from the DNA sequence, leading to a change in the reading frame of the genetic code.

**Option B:** This option is incorrect because nonsense mutations are not typically associated with splice site mutations, which occur when a point mutation affects the splice sites of an intron, leading to abnormal splicing of the pre-mRNA.

**Option C:** This option is incorrect because nonsense mutations are not typically associated with missense mutations, which occur when a point mutation changes a codon to a different amino acid, resulting in a change to the protein product.

**Clinical Pearl / High-Yield Fact**
Nonsense mutations are a common cause of genetic disorders, including cystic fibrosis, sickle cell anemia, and Huntington's disease. These mutations can be identified through genetic testing, which can help diagnose and manage these conditions.

**Correct Answer: A. Nonsense mutation is seen in Cystic Fibrosis.**