Final answer:
The kinetochore is the structure that enables the separation of duplicated chromosomes during the M phase of mitosis, checked by the M checkpoint. This checkpoint ensures that sister chromatids are properly attached to spindle fibers before allowing anaphase to proceed, preventing nondisjunction.
Step-by-step explanation:
The Structure That Allows Separation of Duplicated Chromosomes
The structure responsible for the separation of duplicated eukaryotic chromosomes during the M phase of cell division is the kinetochore. The M checkpoint, also known as the spindle checkpoint, ensures that each sister chromatid is correctly attached to spindle fibers from opposite poles. This checkpoint is critical because the separation of sister chromatids during anaphase is irreversible. If the M checkpoint is not cleared, resulting in improper attachment, nondisjunction of chromosomes can occur, leading to cell division errors. The M checkpoint occurs at the end of the metaphase stage of mitosis, where proper kinetochore function is crucial for successful chromosome segregation.