This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics of Common Disorders, Subject name: Pediatrics
Down syndrome - all are seen except - 
Select and explain. 
A. t (14; 21), B. t (11: 14), C. Trisomy 21, D. t (15: 21)
B: t (11: 14)
Answer: B: t (11: 14) 
Explanation: Ans. is 'b' i.e., t (11: 14) o 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, a 4% have robertsonian translocation.t (13 : 21)t (14 : 21)t (15 : 21)o Very rarely tong arm of chromosome 21 is triplicate (Partial trisomy).