There are several genetic disorders that occur in many organisms where the chromosomes do not separate properly in meiosis which causes the gametes to have an abnormal number of chromosomes (refer to the diagram below). which of the following is the stage where this would occur?

Meiosis is a type of cell division that takes place in the gametes and yields four haploid (n) daughter cells. It takes place in the in two stages namely meiosis I and meiosis II. Non-disjunction is a condition that results from failure of seperation of sister chromatids in mitosis and meiosis I and failure of seperation of homologous chromosomes in meiosis II. The abnormality in meiosis occurs in Anaphase I of meiosis I and Anaphase II of meiosis II, this causes an abnormality in the gametes formed where they end up with abnormal number of chromosomes.

That would be a working theory.