<P> The G / M checkpoint is where the cell ensures that it has enough cytoplasm and phospholipids for two daughter cells . But sometimes more importantly, it checks to see if it is the right time to replicate . There are some situations where many cells need to all replicate simultaneously (for example, a growing embryo should have a symmetric cell distribution until it reaches the mid-blastula transition). This is done by controlling the G / M checkpoint . </P> <P> The metaphase checkpoint is a fairly minor checkpoint, in that once a cell is in metaphase, it has committed to undergoing mitosis . However that's not to say it isn't important . In this checkpoint, the cell checks to ensure that the spindle has formed and that all of the chromosomes are aligned at the spindle equator before anaphase begins . </P> <P> While these are the three "main" checkpoints, not all cells have to pass through each of these checkpoints in this order to replicate . Many types of cancer are caused by mutations that allow the cells to speed through the various checkpoints or even skip them altogether . Going from S to M to S phase almost consecutively . Because these cells have lost their checkpoints, any DNA mutations that may have occurred are disregarded and passed on to the daughter cells . This is one reason why cancer cells have a tendency to exponentially accrue mutations . Aside from cancer cells, many fully differentiated cell types no longer replicate so they leave the cell cycle and stay in G until their death . Thus removing the need for cellular checkpoints . An alternative model of the cell cycle response to DNA damage has also been proposed, known as the postreplication checkpoint . </P> <P> Checkpoint regulation plays an important role in an organism's development . In sexual reproduction, when egg fertilization occurs, when the sperm binds to the egg, it releases signalling factors that notify the egg that it has been fertilized . Among other things, this induces the now fertilized oocyte to return from its previously dormant, G, state back into the cell cycle and on to mitotic replication and division . </P>

List four types of controls on cell cycle rate