A 22-year-old male presents with difficulty walking, impaired speech, and involuntary movements. His father and paternal grandfather had similar symptoms. Genetic testing reveals an expansion of trinucleotide repeats (CAG) in a specific gene. This is an example of which genetic phenomenon?

The correct answer to the question "A 22-year-old male presents with difficulty walking, impaired speech, and involuntary movements. His father and paternal grandfather had similar symptoms. Genetic testing reveals an expansion of trinucleotide repeats (CAG) in a specific gene. This is an example of which genetic phenomenon?" is Option B: Anticipation.

The other options — A) Imprinting, C) Mosaicism, D) Mitochondrial inheritance — are incorrect for this USMLE Exam Prep question. As explained above: Anticipation is a phenomenon where a genetic disorder's symptoms become more severe and/or appear at an earlier age in successive generations. This is characteristic of trinucleotide repeat disorders…