How to determine the cause of Aneuploidy?

[Meadhbh52]

Aneuploidy is when there is an abnormal number of chromosomes in a haploid set. It can be caused by A: meiotic errors during gamete formation

                                                                                                                                                                                        B: mitotic errors in the post-zygotic period.

But how can you distinguish if the aneuploidy is caused by A or B??