This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Single Gene Disorders, Subject name: Pathology
Increasing severity of mental retardation in male members over generations is a result of: 
Select and explain. 
A. Mitochondrial DNA mutation, B. Frameshift mutation, C. Y-linked disorder, D. Trinucleotide repeat mutation
D: Trinucleotide repeat mutation
Answer: D: Trinucleotide repeat mutation 
Explanation: Anticipation Increasing severity of disease in successive generations Trinucleotide repeats cause worsening of clinical features with each successive generation.