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: Pediatrics
Male downs syndrome genotype? 
Select and explain. 
A. 46 XY, B. 47 XY, C. 45 XY, D. 47 XXY
B: 47 XY
Answer: B: 47 XY 
Explanation: Ans. is 'b' i.e., 47 XY In 95% of cases of Down syndrome-trisomy of 21:? Extra chromosome is of maternal in origin. 1% have mosaic with some all have 46 chromosome. 4% have robesonian translocation. t (13 : 21) t (14 : 21) at (15 : 21) Very rarely long arm of chromosome 21 is triplicate (Paial trisomy).