question: Q:A 3-year-old boy presents to a geneticist for generalized developmental delay. Upon presentation he is found to have a distinctive facial structure with prominent epicanthal folds and macroglossia. Further physical examination reveals a simian crease on his palms bilaterally. Based on these findings, the physician strongly suspects Down syndrome and obtains a karyotype. Surprisingly the karyotype shows 46 chromosomes with two normal appearing alleles of chromosome 21. Further examination with fluorescent probes reveals a third copy of chromosome 21 genes that have been incorporated into another chromosome. What is the name of this mechanism of Down syndrome inheritance?? 
  {'A': 'Nondisjunction', 'B': 'Mosaicism', 'C': 'Robertsonian translocation', 'D': 'Imprinting', 'E': 'Anticipation'},