This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'Single gene disorder which does not follow Mendelian inheritance - \nSelect and explain. \nA. Sickle cell anemia, B. Down syndrome, C. Fragile X-syndrome, D. Retinoblastoma', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Transmission of certain single-gene disorders does not follow classical Mendelian principles.\nThis group of the disorder can be classified into the following categories -\n\n\nDiseases caused by triplet - repeat mutation, e.g. fragile - X syndrome, Huntington disease, & others.\nDisorders caused by a mutation in mitochondrial genes, e.g. labour hereditary optic neuropathy.\nA disorder associated with genomic imprinting.\nDisorders associated with gonadal mosaicism.', 'role': 'assistant'}]