Which checkpoint assesses the attachment of spindle fibers to sister chromatids?

The M checkpoint, also known as the spindle checkpoint, specifically assesses the attachment of spindle fibers to sister chromatids during the metaphase stage of mitosis. This checkpoint ensures that all chromosomes are properly aligned and attached to the spindle apparatus before proceeding to anaphase. It is critical for the accuracy of cell division, as it helps prevent errors such as aneuploidy, where cells have an abnormal number of chromosomes.

During this checkpoint, the cell checks that all kinetochores, which are protein structures on the chromatids, are correctly bound to microtubules of the spindle apparatus. If any kinetochores are not properly attached, the checkpoint will halt progression to ensure that the error is corrected. This mechanism is vital for maintaining genomic stability in daughter cells.

Other checkpoints, such as the G1 and G2 checkpoints, are focused on different aspects of the cell cycle. The G1 checkpoint monitors cell size, nutrient availability, and DNA integrity before DNA replication, while the G2 checkpoint ensures that DNA has been accurately replicated and is free of damage before mitosis begins. Checkpoint 3 is not a standard term in cell cycle regulation, making it less relevant in this context. Thus, the M checkpoint is distinctly associated