**Core Concept**
Trinucleotide repeat expansion is a phenomenon where a sequence of three nucleotides is repeated multiple times in a gene, leading to an increase in the number of repeats over generations. This expansion is associated with a variety of neurological disorders, including Huntington's disease and fragile X syndrome.

**Why the Correct Answer is Right**
Trinucleotide repeat expansions occur due to the instability of the repeats during DNA replication and repair. This instability leads to an increase in the number of repeats over time, which can result in the production of a toxic protein that causes cellular damage. The expansion of trinucleotide repeats is a hallmark of several neurodegenerative disorders, including Huntington's disease, which is caused by an expansion of CAG repeats in the Huntingtin gene. The anticipation phenomenon is characterized by an earlier onset and increased severity of the disease in successive generations, likely due to the increased number of repeats.

**Why Each Wrong Option is Incorrect**
* **Option A:** Mitochondrial inheritance refers to the passing of mitochondrial DNA from one generation to the next, which can lead to disorders such as Leber hereditary optic neuropathy. However, it is not associated with the anticipation phenomenon.
* **Option B:** X-linked dominant disorders are caused by mutations in genes on the X chromosome, which can lead to conditions such as Rett syndrome. While X-linked dominant disorders can exhibit anticipation, it is not a characteristic of these disorders.
* **Option D:** Genomic imprinting is the phenomenon where the expression of a gene is determined by its parental origin, which can lead to disorders such as Prader-Willi syndrome. However, it is not associated with the anticipation phenomenon.

**Clinical Pearl / High-Yield Fact**
Trinucleotide repeat expansions can lead to a phenomenon called anticipation, where the disease becomes more severe and appears at an earlier age in successive generations. This is likely due to the increased number of repeats, which can result in the production of a more toxic protein.

**✓ Correct Answer: C. Trinucleotide repeat expansion**