Amitosis: Definition, Mechanism and Examples

Amitosis: What is the purpose of cell division? In general, the purpose of cell division is considered to be multiplicative in unicellular organisms, whereas it is associated with tissue growth and maintenance in multicellular organisms. Can there be a third purpose of cell division? Amitosis is one such kind of cell division that performs specific functions along with reproductive and growth associated actions. According to recent findings, the word amitosis implies merely an absence of mitosis, but the function of amitosis is diverse. Some unicellular organisms such as bacteria, protozoa and yeast etc., reproduce asexually by this process. In this article, we will discuss about Amitosis, its definition, mechanism, examples, etc., in detail.

Definition

In general, the process by which a parent cell divides into two or more daughter cells is known as cell division. It is a necessary biological process that is required for reproduction, growth and development. Cell division involves:

1. Indirect division: Mitosis, Meiosis
2. Direct division: Amitosis

Amitosis is a kind of direct cell division in which the parent cell’s nuclear and cytoplasmic contents are divided between two daughter cells by a simple cell constriction.

The cytokinesis begins after the karyokinesis due to deepening in the cell furrow during amitosis. It does not involve typical events of mitosis such as chromatin condensation, chromatid separation, spindle formation etc.

The emergence of a cleavage furrow or cell constriction identifies the amitosis process. The process of amitosis may occur horizontally or vertically in microorganisms.

Amitosis entails the replication of DNA and the division of the cell. It is a primordial kind of cell division in which a pre-existing cell undergoes a simple mass division. Unlike mitosis, a parent cell does not go through prophase, metaphase, anaphase, and telophase stages.

Fig: Diagramatic Representation of Amitosis

Characteristic Features of Amitosis

The characteristic features of amitosis can be described as follows:

1. Absence of formation of spindle fibres during cell division.
2. Absence of chromatin condensation.
3. The chromosomes do not appear as chromatids.
4. Centromeres do not appear distinctly.
5. Chromatin fibre does not replicate.
6. The nuclear membrane andnucleolusremain intact during cell division.
7. Daughter cells form by the direct deepening of the cell furrow.
8. Random or unequal distribution of the parental chromosomes occurs.

Mechanism of Amitosis Cell Division

Amitosis does not involve many nuclear events. It involves a simple mass division of a pre-existing cell via central cell constriction. The individuals produced after the fission of a parental cell are called daughter cells or nascent cells, while the dividing cell is called a parent or pre-existing cell. The events of amitosis are discussed below:

Fig: Process of Amitosis

1. Elongation of Parent Cell Nucleus: The nucleus of the parent cell elongates.
2. Elongated nuclei form dumbbelllike appearance due to the accumulation of nuclear material at both ends.
3. Replication of DNA: DNA forms its copy by replication inside the nucleus. As a result, DNA doubles itself.
4. Karyokinesis: The nucleus separates into two nuclei with unequal DNA content.
5. Cytokinesis: After the separation of the nucleus, the cytoplasm starts to constrict centripetally, forming a furrow like structure. The gradual inward cytoplasmic constriction leads to the division of the cell.

Amitosis Functions

Amitosis can perform reproductive, developmental or physiological functions.

1. Amitosis as Reproductive function: Reproduction in some organisms like algae, bacteria, cyanobacteria, protozoans, and yeasts occur through amitosis.
2. Amitosis as Developmental function: In mammals like humans, adrenal cells and the placental tissue of rats are observed to divide by amitosis.
3. Amitosis as Physiological function: It occurs in the hepato-pancreas of the crustacean Porcellio. Once the organ reaches maturity, the number of cells in it is never increased. All cells become binucleate when the nucleus undergoes amitotic division

Significance of Amitosis

The significance of amitosis is listed below:

1. Amitosis is a cellular division required for acellular or unicellular organisms to continue their existence.
2. Random distribution of genetic material leads to variation, which is an important tool for evolution.
3. Amitosis is necessary for the production of new cells and bodies as well as the removal of old and damaged cells.
4. It is necessary for the evolution of new species and cell renewal.

Disadvantages of Amitosis

Amitosis, also known as direct cellular fission, has certain disadvantages, which are listed below:

1. Unequal distribution of chromatin: Genetic material between the two growing cells is divided unequally due to the absence of nuclear processes.
2. Irregularities in growth and metabolism: Unequal division in amitosis causes specific irregularities in growth and metabolism.

Examples of Amitosis

Many species and eukaryotic cells, including those listed below, perform amitotic cell division:

1. It is primarily found in unicellular organisms such as algae, protozoans, and bacteria.
2. Amitosis is also carried out by unicellular fungi, such as yeast cells.
3. Eukaryotic cells such as cartilage cells, foetal cells, and extra-embryonic cells also perform amitosis.
4. Amitosis has also been observed in the endosperm cells of seeds in plants.

Difference Between Amitosis and Mitosis

Summary

Amitosis is a kind of direct cell division in which the parent cell’s nuclear and cytoplasmic contents are divided between two daughter cells by a simple cell constriction. It is a type of asexual reproduction among unicellular organisms like algae, bacteria, cyanobacteria, protozoans, and yeasts. It also has developmental and physiological functions. Amitosis can be characterized by features like the absence of formation of spindle fibres during cell division, absence of chromatin condensation etc. The mechanism is simpler than mitosis and involves simpler steps: elongation of the nucleus, replication, karyokinesis, followed by cytokinesis. It is a cellular division required for acellular or unicellular organisms to continue their existence. Amitosis has certain disadvantages, such as unequal distribution of genetic material, which could result in irregular growth and metabolism. It occurs in acellular or unicellular microorganisms like bacteria, yeast etc., primarily, but it also occurs in some plant or animal cells.

Frequently Asked Question (FAQs) on Amitosis

Q.1. What is an amitosis example?
Ans: Amitosis occurs in acellular or unicellular microorganisms like bacteria, yeast etc., primarily, but it also occurs in some plant or animal cells.

Q.2. What is the main difference between mitosis and amitosis?
Ans: The main difference between mitosis and amitosis is that mitosis involves equal division of cells and it performs reproductive and developmental functions, whereas amitosis involves unequal division of cells and it performs the physiological, reproductive and developmental functions.

Q.3. Is there DNA replication in amitosis?
Ans: Yes! DNA replication in amitosis is not similar to mitosis.

Q.4. What is the importance of amitosis?
Ans: Amitosis allows random distribution of genetic material, which leads to variation.

Q.5. Is amitosis faster than mitosis?
Ans: Yes! Based on studies, it has been observed that amitosis is faster than mitosis.

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