A Baby Is Born with What the Physician Believes Is $\mathrm{X}$

A baby is born with what the physician believes is a diagnosis of trisomy 21 . This means that the infant has three number 21 chromosomes. What factor describes the etiology of this genetic change?

A) The mother also has genetic mutation of chromosome 21 .
B) The patient has a nondisjunction occurring during meiosis.
C) During meiosis, a reduction of chromosomes resulted in 23 .
D) The patient will have a single $\mathrm{X}$ chromosome and infertility.