Mitosis is the process of a cell dividing into two daughter cells with duplicate copies of DNA. This occurs rapidly in the tip of an onion root. Many biology courses use specifically onion root tips mounted on microscope slides to demonstrate how this process works in all living things because of an onions fast growth rate and how are relatively large the cells are.
The interphase is the normal state of most of the cells in an onion root. This is where only one cell nucleus is present and one set of chromosomes. During the late part of this phase the chromosomes will start to replicate in the nucleus preparing for replication and division in the next phase.
The prophase is where mitosis really starts. As the chromosomes begin to grow they move and coil up. Fibers and microtubules are grown between duplicated cell parts to align them together. By the end of the prophase the duplicated chromosomes are visible under a microscope. They are lined up in the center of the cell and look similar to the letter x.
As the metaphase begins, the duplicate chromosomes line up in on fibers in the center of the cell parallel to each other so that each side of the cell has one set of chromosomes. At the the end of this phase the fibers grow to be attached to the opposite poles of the cell wall keeping the chromosomes in alignment.
The anaphase marks the separation of both sets of chromosomes. This is when each set starts to move down the fibers in opposite directions to the opposite poles of the cell wall in preparation for creating two individual nuclei.
As the two sets of chromosomes cluster on opposite ends of the cell they form individual daughter nuclei. The cell membrane then grows around each nuclei until the cells separate and a new cell wall grows between them. This forms two identical daughter cells which will be in the interphase. As this process continues, more and more layers in the root tip are formed.