Fred and Mary have a child with Down syndrome. A probe derived from chromosome 21 was used to identify RFLPs in Fred, Mary, and the child (darker bands indicate signals of twice the intensity)....

Fred and Mary have a child with Down syndrome. A probe derived from chromosome 21 was used to identify RFLPs in Fred, Mary, and the child (darker bands indicate signals of twice the intensity). Explain what kind of nondisjunction events must have occurred to produce the child if the child’s RFLP pattern looked like that in lanes A, B, C, or D of the following figure: