Mitosis in an Onion Root Tip

The process of mitosis is cell reproduction of "regular" body cells. (Note: This is not sex cell reproduction.) Mitosis in an onion root cell is a common type of cell to view under the microscope because it is large and often you can view many different stages of mitosis in a single section of onion root tip. It is also common to stain the cells slightly to make the chromosomes more visible. The student will be looking for cells undergoing Interphase, prophase, metaphase, anaphase, and telophase.

Interphase: is the stage of mitosis where the cell looks like nothing is really happening. In this phase the DNA material is duplicating, but not visible. The nucleus of the cell is still clearly visible and the nuclear membrane has not broken down.

Prophase: During this stage of mitosis the nuclear membrane breaks down and the chromosomes start to move more toward the center of the cell but in a midline arrangement, but they are more like a ball of chromosomes at this point.

Metaphase: During this stage the chromosomes are clearly lined up in a midline formation. In some cases you may see "spindle fibers" attached to the chromosomes and that go toward the pole ends of the cell.

Anaphase: During this stage the chromosomes have begun to moe away from the midline. They are moving toward opposite poles of the cell.

Telophase: During this stage the chromosomes have moved to their respective poles and a pinching of the side walls of the cell may be visible. The nuclear membrane may be starting to form. Soon the original one cell will become two cells.

By using a diagram like the graphic with students they can try to identify the stages depicted in the graphic. When I have made this graphic for use in class I have put a lot more chromosomes and a lot more cells into the graphic, but this version should give you the idea. Sometimes a biology teacher might use a swab to get cheek cells from a student in the class to show under the microscope. Cheek cells are also rather large, but they really must be stained because they are so clear that the chromosomes when unstained will be very difficult to observe. It is a bit less likely to use a cheek swab in today's classroom because you are then dealing with "bodily fluids". If you should decide to try this be absolutely certain you know how to do this safely and that you throw away the swab immediately after collecting the first specimen. You will want to stain the specimen and use a cover slip on the slide. (Note: This is not spit on the slide, by scraping the cheek slightly with the swab you actually dislodge cells from the skin of the cheek.) Purchasing commercially prepared slides may provide the best way to observe mitosis because of the better staining techniques used.