Mitosis in Onions and Meiosis in Gametes
The cells in every organism must make copies of themselves so that the organism may grow and reproduce. The cells in an adult human are about the same size as that in a newborn baby’s body. Because of this, every organism needs mitosis (the ability for cells to make copies of themselves) and meiosis (the making of gamete cells).
Mitosis is a four stage cycle where cells make copies of their chromosomes, pull these copies apart, and create two new daughter cells. The pre-stage, Interphase, is when the cell grows, does its specific job, and prepares for mitosis. The first stage, Prophase, is when the nucleus becomes visible and the centrioles begin to move towards opposite sides of the cell. Next, in Metaphase, spindle fibers align the chromosomes in the center of the cell. Anaphase then begins, and the chromosomes pull apart to opposite sides of the cell. Finally, Telophase begins. The chromosomes are on opposite sides and start to form two daughter cells. Simultaneously, Cytokinesis occurs and the two cells pinch apart with their own membranes and nuclei. Once this phase is complete, the cell goes into the G1, S, and G2 phases.
We saw Mitosis in the two labs we constructed with onion roots. We had a lab where the onion root tips were prepared slides, meaning that they were created for viewing mitosis and all four stages of it. The second lab was one where we grew our own onion roots and prepared our own slides from these. In the first lab, most cells were going through mitosis. We were able to see all of the stages very easily. In the second lab, however, it was difficult to find more than six or seven cells that had entered mitosis.
Meiosis is the process in which cells produce gamete cells so that an organism can reproduce. It begins with a diploid cell making copies of its chromosomes that “cross-over” and becoming two daughter cells. These daughter cells split once again, but do not make copies of...