Binary fission
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Binary fission is the form of asexual reproduction in single-celled organisms by which one cell divides into two cells of the same size, used by most prokaryotes. This process results in the reproduction of a living cell by division into two equal or near-equal parts.
Mitosis is not the same as binary fission.
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[edit] Genetic effects
Binary fission is asexual; the organism splits directly into two equal-sized offsprings, each with a copy of the parent's genetic material. Binary fission is a common type of reproduction in single-celled organisms.
Bacterial DNA has a relatively high mutation rate. This rapid rate of genetic change is what makes bacteria capable of developing resistance to antibiotics and helps them exploit invasion into a wide range of environments.
Organisms that reproduce through binary fission generally have exponential growth phases. Escherichia coli cells are able to divide every 20 minutes under optimum conditions.
[edit] Process
Binary fission begins with DNA replication. DNA replication starts from an origin of replication, which opens up into a replication bubble (note: prokaryotic DNA replication usually has only 1 origin of replication, whereas eukaryotes have multiple origins of replication). The replication bubble separates the DNA double strand, each strand acts as template for synthesis of a daughter strand by semiconservative replication, until the entire prokaryotic DNA is duplicated.
After this replicational process, cell growth occurs.
Each circular DNA strand then attaches to the cell membrane. The cell elongates, causing the two chromosomes to separate.
Cell division in bacteria is controlled by the septal ring, a collection of about a dozen proteins that collect around the site of division. There, they direct assembly of the division septum.the cell wall and plasma membrane starts growing transversely from near the middle of the dividing cell. The dividing septum originates centripetally and separates the parent cell into two nearly equal daughter cells ,each having a nuclear body [1]
The cell membrane then invaginates (grows inwards) and splits the cell into two daughter cells, separated by a newly grown cell plate. This process is called cytokinesis.
[edit] Organisms using binary fission
Many organisms reproduce by binary fission, such as:
Some eukaryotes reproduce using binary fission-like methods. Mitosis is thought to derive from binary fission.
[edit] Binary fission in protozoans
In binary fission in protozoans, the replicated chromosomes are separated by intranuclear (closed) mitosis and the nucleus divides by furrowing. The cytoplasm then gradually constricts between the two separating nuclei, ultimately forming two equally sized daughter individuals, each with a nucleus. The offspring grows to the size of the parent before dividing again.
[edit] Types of binary fission
Binary fission is mainly of three types with regard to the plane of division:
- Irregular binary fission: Occurs in amoebae. The plane of division of cytoplasm varies but is always at right angles to the elongated dividing nucleus.
- Longitudinal binary fission: Occurs in flagellates such as Euglena. The cytoplasm splits lengthwise, from forward to backward, forming two similar daughter individuals.
- Transverse binary fission: Occurs in ciliates such as paramecium. The cytoplasm divides transversely between two sets of nuclei, forming two dissimilar individuals. This is called bacterial fission.
