Which statement best describes the M checkpoint?

Which statement best describes the M checkpoint?

• A. A checkpoint that ensures the cell has achieved sufficient size to divide.
• B. A checkpoint that ensures DNA replication is complete before mitosis.
• C. A checkpoint that confirms all sister chromatids are correctly attached to the mitotic spindle before cell division is completed.
• D. A checkpoint that monitors cytokinesis timing.

Answer: (C)

The M checkpoint, also known as the spindle assembly checkpoint, monitors chromosome attachment and tension at the mitotic spindle. Its role is to ensure that every chromosome’s sister chromatids are properly attached to spindle microtubules via kinetochores before anaphase begins and cell division proceeds. If even one chromosome isn’t correctly attached, the checkpoint halts progression, preventing mis-segregation and aneuploidy. This is why the statement describing the checkpoint as confirming that all sister chromatids are correctly attached to the mitotic spindle before cell division is completed is the best description. Other options describe checkpoints at other stages—such as cell growth size before division, completion of DNA replication, or cytokinesis timing—which are not the spindle assembly checkpoint.

The M checkpoint, also known as the spindle assembly checkpoint, monitors chromosome attachment and tension at the mitotic spindle. Its role is to ensure that every chromosome’s sister chromatids are properly attached to spindle microtubules via kinetochores before anaphase begins and cell division proceeds. If even one chromosome isn’t correctly attached, the checkpoint halts progression, preventing mis-segregation and aneuploidy. This is why the statement describing the checkpoint as confirming that all sister chromatids are correctly attached to the mitotic spindle before cell division is completed is the best description. Other options describe checkpoints at other stages—such as cell growth size before division, completion of DNA replication, or cytokinesis timing—which are not the spindle assembly checkpoint.