**Core Concept:**
Frame shift mutation is a type of genetic mutation that occurs when a single nucleotide in the DNA sequence is inserted, deleted or replaced, causing a shift in the reading frame of the mRNA molecule. This results in the production of an abnormal protein due to alterations in the subsequent amino acid sequence.

**Why the Correct Answer is Right:**
The correct answer is **D**. In the case of a frame shift mutation, a single nucleotide substitution leads to the alteration of the reading frame of the mRNA molecule. When an adenine (A) is inserted, deleted, or replaced by another nucleotide, the subsequent nucleotides will be shifted by two bases, resulting in a change in the amino acid sequence. This alteration in the protein sequence can lead to a loss of function, dominant negative effect, or increased toxicity, ultimately causing a genetic disorder or disease.

**Why Each Wrong Option is Incorrect:**
Option A represents a point mutation, where a single nucleotide change leads to a change in a single amino acid residue. This does not result in a shift in the reading frame of the mRNA molecule, making it an incorrect answer for frame shift mutation.

Option B represents a small deletion or insertion of nucleotides, which does not directly affect the reading frame of the mRNA molecule. This is also incorrect for a frame shift mutation.

Option C represents a large deletion or duplication of nucleotides, which could potentially impact the reading frame, but is not as direct or consistent as a single nucleotide substitution causing a two-base shift in the mRNA molecule. This is also incorrect for a frame shift mutation.

**Clinical Pearl / High-Yield Fact:**
Frame shift mutations are associated with a wide range of genetic disorders, including cystic fibrosis, sickle cell anemia, and hereditary hemorrhagic telangiectasia. Understanding the mechanisms of genetic mutations is essential for diagnosing, treating, and counseling patients with genetic disorders.