Answer
a) During anaphase I or anaphase II
b) During anaphase, one of the gametes lost a chromosome 14 but gained an extra chromosome 21
Work Step by Step
a) Non-disjunction occurs during both anaphases in meiosis. This is because the spindles do not correctly pull the right amount of chromosomes to a pole
b) In the specific case of down syndrome, one of the gametes lost a chromosome 14 but gained an extra chromosome 21. This results in a total number of 46 chromosomes
