Please see image. Aneuploids occur when chromosomes/chromatids fail to separate during a meiotic anaphase, sending more chromosomes to one daughter cell than to the other. The image shows two homologous chromosomes (indicated by two styles of lines). Anaphase I nondisjunction sends four copies of a chromosome (as attached chromatids) to one daughter cell and none to the other. Anaphase II nondisjunction sends two copies to one daughter cell/gamete and none to the other.
Work Step by Step
To get to this answer, remember that the question indicates that nondisjunction can happen in meiosis I or II, and, since it involves a lack of chromosomal separation, this must occur in anaphase. Then, draw two cells, one in anaphase I, and the other in anaphase II. Have all the chromosomes from one pair or set of 4 (anaphase II and I, respectively) moving to one pole and none to the other.