This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics, Subject name: Pathology
Increasing severity of mental retardation of 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: Ans. (d) Trinucleotide repeat mutation(Ref: Robbins 9th/pg 168-171; 8th/pg 168-171)Increasing severity of mental retardation of male members over generations is a result of "anticipation", seen in disorders caused by Trinucleotide repeat mutation. Eg Fragile X syndrome