A baby is born with the clinical characteristics of trisomy 21. C-banding is used to examine the chromosomes of the baby. The father has a C-banding polymorphism that distinguishes both his chromosome 21's from each other, and the mother's chromosome 21s as well. The mother's chromosome 21s cannot be distinguished by this banding technique. When the baby's chromosome 21s are examined in metaphase spreads three uniquely banded chromosomes are identified. This data indicates that the non-disjunction event occurred most likely in which ONE of the following?
A. Paternal meiosis I
B. Maternal meiosis I
C. Meiosis II of either parent
D. During mitosis during early embryogenesis
E. Cannot be determined from the data given