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
This gene mapping indicates: 
Select and explain. 
A. Klinefelter syndrome, B. Cri du chat syndrome, C. Eagle’s syndrome, D. Down’s syndrome
D: Down’s syndrome
Answer: D: Down’s syndrome 
Explanation: Down's syndrome, which is due to trisomy of chromosome 21 (XXX).