Cell Division: Binary Fission, Mitosis & Meiosis

Cells are the most fundamental units of life. All living organisms are made of one or more. Cells reproduce by copying their genetic material and then dividing—a parent cell giving rise to daughter cells.
Although these basics of cell division are the same for all forms of life, there are important differences between prokaryotes and eukaryotes, as well as between somatic cells and germ cells.

What Is Binary Fission?

The reproduction of prokaryotic cells (bacteria and bacteria-like Archaea) is accomplished through binary fission. A bacterial cell that is ready to divide first copies its genetic material, called the nucleoid—a single, circular chromosome of DNA (deoxyribonucleic acid). The two chromosomes, each attached to the plasma membrane, move apart as the cell elongates. Once the two copies of genetic instructions are separated, the cell divides, laying down new cell wall and membrane between the two chromosomes.
Binary fission is essentially cloning. Barring mutations that may have occurred when the genetic material was copied (a process called replication), the two resulting daughter cells are identical to the parent cell. How frequently a bacterium undergoes cell division is known as generation time, and, even under optimal conditions, the time required varies widely among bacteria.

What Is Mitosis?

Mitosis is division of the somatic cells of eukaryotic organisms. Somatic cells are all cells of the body, other than the reproductive cells of sexually reproducing organisms—sperm and egg.
Although more complicated in it timing and execution, and involving more DNA, the basic result of mitosis is the same as that of binary fission—chomosomes are replicated, copies are moved to opposite ends of the parent cell, and then the parent cell divides, giving rise to two daughter cells that are identical to each other and to the parent cell. Mitosis is how single celled eukaryotic organisms reproduce, and how multi-cellular eukaryotes develop, grow, and repair.

The stages of mitosis include the following:

• Interphase: The cell is carrying out day-to-day functions, and preparing to divide. The S Phase (S for synthesis) of interphase is the point at which chromosomes are duplicated in preparation for cell division.
• Prophase: Each set of duplicated chromosomes (celled sister chromatids), condense and the mitotic spindle forms and attaches to each sister chromatid.
• Metaphase: Sister chromatids line up at the cell equator.
• Anaphase: Sister chromatids are pulled apart, and, once separated, are known as daughter chromosomes. The spindle pulls each daughter chromosome to opposite sides of the cell.
• Telophase: A complete copy of the genome arrives at each end of the cell. Cytokinesis, the actual division of the cell, takes place, and chromosomes decondense.

Mitosis results in two daughter cells that, if without mutation, are identical to the parent cell that generated them.

What is Meiosis?

Meiosis is the production of sperm and eggs in sexually reproducing individuals. The process of meiosis reduces the chromosome number by half, so that when a sperm fertilizes an egg, the resulting zygote has a full set of chromosomes. During meiosis there are two cell divisions of a diploid (2n) parent cell, resulting in four haploid (n) gametes.
For details on the steps of meiosis, see the article” Meiosis & Sexual Reproduction: How Sex Cell Formation and Fertilization Shuffle Our Genes.” To learn more about cell biology in general, see the science education website Science Prof Online.
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Sources

Campbell, N. A. & Reece J. B. (2005) Biology, seventh edition. Pearson Education Inc.
Campbell, N. A., Reece J. B. & Simon, E. (2004) Essential Biology with Physiology. Pearson Education Inc.