What the Heck does 'Mitosis' Mean?

Every time a cell divides, it must ensure that its DNA (packaged into chromosomes) is faithfully partitioned between the two daughter cells. Mitosis is the process of 'divvying up' the genome between dividing cells. What follows is a simple guide for those unfamiliar with cell division and mitosis.

To make this simple, let's imagine a cell with only one chromosome. Before a cell enters mitosis, we say the cell is in interphase:

Every time a cell divides, it must first replicate all its DNA. Since chromosomes are simply DNA wrapped around protein, the cell replicates its chromosomes too:

These two chromosomes, positioned side by side, are called sister chromatids. They are identical copies of one another. Before this cell can divide, it must separate these sister chromatids from one another.

First off, these chromosomes have to condense in a process called prophase:

And then, the nuclear envelope breaks down:

Then a large protein network called the spindle attaches to each sister chromatid and the chromosomes are aligned perpendicular to the spindle in a process called metaphase:

Next, molecular motors pull the chromosomes away from the metaphase plate to the spindle poles of the cell. This is called anaphase:

Once this process is completed, the cells divide, the nuclear envelope reforms, and the chromosomes relax and decondense during telophase. Then the cell can replicate its DNA again during interphase and go through mitosis once more.