Binary fission could be defined as a mode of asexual reproduction by which an organism separates into two parts each carrying its own genetic material. If we further define binary fission, it is the primary method of reproduction in a prokaryotic organism. It is often classified into transverse longitudinal and oblique types based on the axis of the cell separation.
Transverse binary fission in organisms like scyphistoma polyps, tapeworms are called strobilation. This type of fission results in strobilus in these organisms. The ephyrae of the scyphozoan jellyfish and the proglottid of the tapeworms mature and separate from the strobilus. In a few metazoan species, their body undergoes division on a regular basis in a process called fragmentation and each fragmented part develops to a new organism.
Examples of binary fission can be observed in bacteria, amoeba, and in several eukaryotic cell organelles.
There are four types of binary fission known. These are
Irregular binary fission
Transverse binary fission
Oblique binary fission
Longitudinal binary fission
In this type of binary fission, cytokinesis takes place along a perpendicular plane to that of Karyokinesis. The plane of cytokinesis is always perpendicular to the plane on which Karyokinesis is observed. One classic example of irregular binary fission is the reproduction in amoeba.
Irregular Binary Fission In Amoeba
One of the species under this class is the Amoeba proteus. It lacks a definite shape and moves through temporary projections called pseudopodia. Like many prokaryotic organisms, it also reproduces through binary fission.
The genetic material is replicated through mitotic division and the cell divides into two daughter cells. At the end of the telophase, two daughter nuclei are formed with a lattice that forms beneath each nuclear membrane. The two daughter cells that are produced are genetically identical.
In this type of binary fission, the cytokinesis phase of cell division takes place along the transverse axis. It can be observed in paramecium.
Binary fission in paramecium:
In paramecium, reproduction takes place by asexual means and mainly through transverse binary fission. This eukaryotic organism has two nuclei, a large macronucleus, and a small micronucleus. The micronucleus is responsible for reproduction.
In favorable environmental conditions, the ciliate structure of the cell stops feeding and the oral groove disappears. The micronucleus divides into two micronuclei which move towards the pole ends of the cell. Afterward, the macronucleus divides into two and the two move to either end of the cell. Then cytokinesis takes place along the transverse axis of the cell giving rise to two daughter cells.
It should be noted that the micronucleus of the paramecium divides trough mitosis whereas the macronucleus divides through amitosis.
This type of binary fission takes place in more than one way. It can be observed in Ceratium where the organisms shell pulls apart at first and it exposes the naked cell. Then the cell size increases and divides into 4-8 cells each with two flagella. The nuclear membrane is present throughout the process and it only divides when the waist of the organism constricts.
When binary fission takes place along the longitudinal axis of a cell it is called longitudinal bacterial fission. It can be observed in Euglena. The cell division starts at the front end of the cell and continues with the duplication of the flagellar processes, stigma and gullet. At first, a cleavage forms at the anterior part followed by a V-shaped bifurcation towards the posterior part. This continues until the two parts are separated.
Bacteria also reproduce through asexual reproduction and the speed differs between species. The time taken for one bacterial cell to duplicate itself is called doubling time. Factors such as pH levels, temperature, light, oxygen, osmotic pressure play a factor in bacterial reproduction or bacterial binary fission. The following are the steps involved in the binary fission of bacteria.
Genome replication: In bacteria, binary fission starts with the replication of the genome. Replication enzymes copy the chromosome strand at the point of origin and then continue separating the strand in two.
The growth of the cell: After the chromosome is duplicated in two strands, the bacterial cell grows larger and prepares for binary fission. The volume of cytoplasm and cell organelles increase with the cell. Another feature of this stage is that the two chromosome strands migrate to opposite poles of the cell.
The segregation of the genetic material: In this stage, the plasma membrane’s peripheral ring invaginates and divides the mother cell into two. It is accompanied by the formation of a double membranous septum before two cells completely separate in two identical cells.
Splitting into two cells: This stage starts with the development of a cell wall and the cell splits at the center. Afterward, the mother cell divides into two daughter cells. Each daughter cell contains one copy of the genetic material and all necessary cell organelles.
1. What are the benefits and drawbacks of binary fission?
There are many benefits of binary fission,
A single parent is needed to reproduce.
Cells can divide rapidly
Daughter cells are perfect clones of parent cells
A single cell can produce many daughter cells within a limited time.
However, the drawback of binary fission is, there is no genetic recombination within the species and a fissioned cell cannot survive changes in the environment they strive in. However, binary fission stops the overpopulation of bacteria.