EUGENE M. MCCARTHY, PHD GENETICS
|First division of a zygote. (Enlarge)|
Basic diagram of mitosis.
Diagram comparing mitosis with meiosis. Credit: Saperaud|
One of the most dramatic activities that eukaryotic cells accomplish is division, in which a cell must first copy and sort out evenly all of its genetic material (chromosomes), and then pinch itself in two. This process, which produces two genetically identical daughter cells from a single parent cell, is called mitosis.
No change in chromosome number occurs during mitosis, because one sister chromatid from each chromosome in the parent cell passes into each of the two daughter cells (the sister chromatids separate during anaphase).
Mitosis is the method by which the somatic cells of all multicellular organisms multiply (it is the process by which growth occurs). In addition, plants produce gametes by mitosis (they make spores by meiosis). Animals produce gametes via meiosis. The stages of mitosis are detailed on the pages to come. So keep reading!
Overview of mitosis: During the course of the cell cycle interphase and mitosis alternate. During interphase the chromosomes replicate and the cell prepares for mitosis, which is the process of cell division in which one cell becomes two genetically identical daughter cells. During interphase the chromosomes exist as thin, unpacked threads invisible under a light microscope. But during the first stage of mitosis, prophase, the chromosomes pack (condense) into dense visible masses. Then, during metaphase the cellular machinery attaches itself to each chromosome and moves them to the equator of the cell ("metaphase plate"). In anaphase, one sister chromatid from each chromosome is pulled to one of the two opposite ends ("poles") of the cell. During telophase they reach the poles and the cell separates into two daughter cells.
When does mitosis occur? Mitosis occurs only in eukaryotes. It is the process by which the somatic cells of all multicellular organisms multiply. Prokaryotes (archaea and bacteria), which are single-celled, divide by binary fission. In the eukaryotic cell cycle, mitosis alternates with interphase.
Why does mitosis occur? Mitosis allows the equal distribution of chromosomes into daughter cells. The resulting two cells are genetically identical to each other and to the parent cell that divided to produce them. Without the organized process of mitosis, chromosomes would be distributed at random into the daughter cells and the resulting cells would probably not even be viable.