Asexual reproduction, a mode of reproduction, is where organisms produce new offspring without the involvement of a mate. It means there is no fusion of gametes (sperm and egg cells). This process has genetically identical offspring, or clones, because of the same genetic makeup as the parent. There are different types of asexual reproduction, including binary fission, budding, vegetative reproduction, parthenogenesis, and fragmentation.
Binary fission, form of asexual reproduction in which a single mother cell produces two genetically identical clone daughter cells. This type of reproduction mostly takes place in prokaryotes and also in some unicellular eukaryotes. The specific cell organelles in eukaryotes, i.e., mitochondria and chloroplasts, also divide by binary fission.
Although binary fission and mitosis are similar, their purpose is different. Cells undergo mitosis cell division for cell growth or to repair old or worn out cells in multicellular organisms, but binary fission is necessary for reproduction purposes in unicellular organisms.
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Steps of Binary Fission
This asexual reproduction, binary fission, occurs only under favorable conditions which produces two genetically identical offsprings. Binary fission completes within the following steps or processes:
- It begins with the initiation of replication of DNA from the site of origin of replication. The replication is bidirectional and results in duplicate DNA.
- After duplication, cells grow and increase in size. At the same time, various Fts (filamentous temperature sensitive) proteins interact to form a cell division apparatus known as a divisome that begins with the attachment of molecules of Ftsz in a ring around the center of the cell. The divisome forms when the cell is already elongating, and DNA is replicating.
- The Ftsz is the key Fts protein required for cell division. A Ftsz ring formed between two duplicate DNA determines the cell division plane. Similarly, at the beginning of Ftsz ring formation, small gaps in the wall forms by enzymes called autolysin by dissolving the bond between cell wall precursors. As a result, new cell wall material is added across the gap to form a new cell wall.
- As cell elongation continues and septum formation begins, two copies of chromosomes are pulled apart to their own daughter cell, which is assisted by various proteins, including Ftsk or par protein.
- The divisome arranges the synthesis of a new cytoplasmic membrane and cell wall material called the divisome septum as the cell reaches twice its original length.
- After the septum formation is complete, the cell pinches into two, forming two daughter cells. Similarly, Ftsz protein is dispersed throughout the cytoplasm of new daughter cells. The shape of the cell to be formed is determined by MreB protein during cell division. The time required for forming two daughter cells from a single mother cell during binary fission is known as Generation time.
Types and Examples
It has been divided into four types; irregular, longitudinal, transverse, and oblique binary fission.
Irregular Binary Fission:
- Cytokinesis/fission occurs through any plane but perpendicular to the plane of division of chromosomes, known as irregular binary fission.
- This type of binary fission occurs in protozoans, i.e., Amoeba.
Longitudinal Binary Fission:
- Cytokinesis/fission occurs through a longitudinal plane, known as longitudinal binary fission.
- This type of binary fission occurs in protozoan, i.e., Euglena.
Transverse Binary Fission
- The division plane passes along the transverse axis, known as transverse binary fission.,
- This type of binary fission occurs in bacteria, Paramecium and diatoms.
Oblique Binary Fission
- Cytokinesis/fission occurs obliquely, either left or right oblique, known as oblique binary fission.
- This type of binary fission occurs in dinoflagellates, i.e., Ceratium.
- Madigan, M., 2012. Brock Biology of Microorganism. 13th ed. London: Prentice Hall International Inc., pp.118-121.
- Binary fission. Libre Text. Retrieved on 31st July 2022, from https://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Boundless)/6%3A_Culturing_Microorganisms/6.6%3A_Microbial_Growth/6.6A%3A_Binary_Fission