Final answer:
An error in the anaphase stage of mitosis, specifically during the M checkpoint, can lead to unequal numbers of chromosomes in the resulting daughter cells, causing nondisjunction and chromosome disorders.
Step-by-step explanation:
If an unequal number of chromosomes are found at the end of cell division, then there was likely an error during mitosis. The stage of mitosis that most likely went wrong is anaphase. This is the stage during which sister chromatids are supposed to separate and move to opposite poles of the cell.
The M checkpoint, which occurs near the end of the metaphase stage of mitosis, plays a critical role in ensuring that sister chromatids are correctly attached to the spindle microtubules before separation. If there is a failure in this checkpoint, nondisjunction may occur, leading to unequal distribution of chromosomes. This means one daughter cell may end up with an extra chromosome, while the other lacks that chromosome, leading to chromosome disorders in the resulting cells.