Cyclin B is a protein that plays a crucial role in the cell cycle, particularly in the transition from G2 phase to M phase (mitosis). It activates a specific enzyme called cyclin-dependent kinase 1 (CDK1), which is essential for the cell to prepare for division. The levels of cyclin B fluctuate throughout the cell cycle, rising as the cell prepares to divide and falling after mitosis is complete. During mitosis, cyclin B helps regulate various processes, including chromosome alignment and separation. Its proper function is vital for ensuring that cells divide accurately, preventing issues such as aneuploidy, where cells have an abnormal number of chromosomes. This regulation is critical for maintaining healthy cell growth and function.