What causes meiosis to occur?

[BigToque]

All cells in the body can undergo mitosis, however the germ cells can undergo both mitosis and meiosis.

After the germ cell replicates the chromosomes, what causes it to pull the sister chromatids into a new N cell which leads to four gametes, as opposed to splitting them up and just creating a new 2N cell?

Is it just random luck of the draw?

 

[Gigantopithecus]

It varies.

 

[Bill Brasky]

It varies.

lol. Yeah, it varies so much and not all organisms accomplish it in the same manner.

In general, there are two methods: intrinsic, and extrinsic. Intrinsic means the cell has the proper steps coded in it's DNA to execute meiosis, regardless of the outside environment. Extrinsic means the cells require an external signaling molecule, or the lack there of, to change division cycles. Imagine a stationary germ cell on the left. As it divides, daughter cells are pushed away from the germ cell. Then imagine the germ cell emitting a signaling molecule, and once the daughter cells are "out of reach" of the signaling molecule, the divisions change cycles.