Final answer:
The M checkpoint, also known as the spindle checkpoint, ensures correct attachment of sister chromatids to the spindle apparatus and prevents anaphase until all kinetochores are properly anchored. It monitors tension and protein phosphorylation by MPF, and if it fails, it can result in nondisjunction and chromosomal abnormalities.
Step-by-step explanation:
The M checkpoint, also known as the spindle checkpoint, occurs near the end of the metaphase stage of mitosis. This checkpoint is crucial as it ensures that all sister chromatids are correctly attached to the spindle microtubules via their kinetochores. The kinetochores must be firmly anchored to at least two spindle fibers from opposite poles of the cell. If this condition is not met, the cell cycle is halted, preventing the irreversible step of sister chromatids separation during anaphase until the error is corrected.
Additionally, the M checkpoint is involved in monitoring the tension in the spindle apparatus and the phosphorylation of proteins by Maturation Promoting Factor (MPF), leading to the proper segregation of chromatids. Passing the M checkpoint means the cell is ready to complete mitosis and cytokinesis, moving on to the next cell cycle phase.
If the M checkpoint fails, the consequences can be severe, including nondisjunction of chromosomes, which can lead to aneuploidy and other chromosomal abnormalities in the daughter cells.