Well that depends on where the non-disjunction might occur in meiosis; if it occurs in meiosis I then it would be a non-disjunction between pairs of chromosomes, if it occurs during meiosis II then it would mean a non-disjunction between sister chomatids. Non-disjunction refers to a process occurring during (late) metaphase and not specifically during anaphase. Reviewing meiosis would help I think (try drawing it out). Take care mxj

Non-disjunction just applies to the whole process from beginning to end not specifically to one phase of the cycle but the earliest you could say ‘he that chromosome has not separated and starts moving to the wrong pole’ would be late metaphase/early anaphase. The standard phrase is non-disjunction occurring during meiosis I or II. Remember that all these phases flow into each other so one person’s late metaphase could be another’s early anaphase, there’s no point getting into the details of this as long as you understand non-disjunction and the differences between its occurrence in M I and II