Difference Between Cleavage and Mitosis

Cell Cycle Events: Cleavage and Mitosis

Cleavage Definition: Simply stated cleavage is the very simple form of division of cells. It is mainly the cytoplasmic division of the cells. In the case of developmental biology, cleavage is the division of cells in the early embryo - the zygote.

Mitosis Definition: Mitosis is an entire process of cell division where a parent cell divides into daughter cells. It is a stage of the cell cycle divided into five phases that include the replication of the DNA, and subsequent division of the nucleic acid material with the division of the cytoplasm resulting in two daughter cells. 


Cleavage and its Types

From the given cleavage definition above, cleavage meaning in science clearly means a simple division of cells. In a more crude manner, the cleavage definition is the breaking of the cytoplasm of the cell into two new cytoplasms of two new cells. Thus, when asked to define cleavage, it can always be defined as the cytoplasmic division of all of types cells, be it animal cell, plant cell, prokaryotic cell or eukaryotic cell. 

There are four types of cleavage of the cells. They are given below:

Determinate: In this type of cleavage, the daughter cells or the divided cells don't have the capacity to fully generate an individual organism. Instead, all the divided cells combined have the potential to fully generate an individual organism or are part of the whole organism. For example, the division of the cells while the transformation of the zygote to the blastomere stage takes place. All the cells of a zygote together form an embryo while only a single cell out of all of them does not make up the embryo.

Indeterminate: In this type of cleavage, the daughter cells or the divided cells have the capability to fully generate an individual organism. This type of cleavage is part of not only the reproductive process of many unicellular eukaryotic and prokaryotic organisms but also of the cell cycle division process of mitosis. Examples include the cleavage in the reproduction of amoeba, bacteria, etc. 

Holoblastic: In this type of cleavage, the zygote and blastomeres are completely divided during the cleavage. So, after every cleavage, the number of blastomeres doubles in number. When a large concentration of the yolk is absent then the cells with the small and even distribution of the yolk - isolecithal cells or the cells with a moderate concentration of yolk (in gradient distribution) - mesolecithal or microlecithal cells, show four types of cleavage: bilateral (simple bisection into two halves of a single cell around a central axis), radial (cleavage along the spindle axis which are parallel or at right angles to the polar angles of the dividing cells), rotation (an equatorial division of one daughter cell and a meridional division of another daughter cell) and spiral cleavage. 

Meroblastic: This type of cleavage occurs when a large concentration of yolk is present in the cells. Because of the large concentration of the yolk the cells can undergo partial cleavage which is called meroblastic cleavage. 

The diagram below shows the types of holoblastic and meroblastic explaining cleavage meaning in science.


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What is Mitosis and What are its Phases?

Mitosis explanation can be given as: it is a type of cell division and final stage of the cell cycle where one parent cell gives rise to two daughter cells with genetic material identical to the parent cells. It can be differentiated into two steps - nuclear division takes place in the first step and then the cytoplasm is divided or cleaved in the second step. A cell undergoes the following five phases during undergoing mitosis cell division before undergoing cleavage or cytokinesis:

Interphase: In this phase, the copying of the nucleic material in the cell occurs. Providing two identical full sets of the DNA. There are two centromeres located outside the nucleus each containing a pair of centrioles. These centromeres are the anchor points for the origin and extension of microtubules.

Prophase: The diffused chromosomes begin to appear and condense into X-shaped structures, with each structure made up of two sister chromatids containing identical DNA. The nuclear membrane dissolves in this stage and the chromosomes are released from the nucleus. Also, the mitotic spindle formed of the extending microtubules and other proteins grows across the cell between the two centrioles which are now moving to opposite poles of the cell.

Metaphase: The chromosomes are aligned along the equator of the cell and the mitotic spindle fibres extending from the centrioles at the poles attach to each of the sister chromatids in this stage of mitotic cell division.

Anaphase: During this phase of mitosis, the sister chromatids are separated from each other and driven by the spindle fibres to opposite poles of the cell. This marks the clear distinction and end of the division of the nucleic acid material of the parent cells for the two daughter cells. 

Telophase: After the two full-sets of chromosomes are gathered on the opposite poles, a new membrane begins to form around them creating two new nuclei. This organisation and formation of the new nuclei is the characteristic of telophase. Following, the telophase, the cytokinesis or the cleavage of the cell takes place resulting in the formation of two daughter cells with identical parental genetic information. 

The entire process of the five phases of the mitosis is explained clearly in the given below diagram:


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Thus, cleavage differs from mitosis in lacking the duplication and division of the genetic material of the cell.


Difference Between Cleavage and Mitosis

The difference between cleavage and mitosis is given below in a tabulated format.

Cleavage

Mitosis

There can be a decrease in the size of the cells after cleavage. For example: In the case of blastomere cleavage, the cells divide rapidly and as they increase by division in number their single cell (after division) size decreases.

There is no size change after the mitosis cell division as the daughter cells continue to grow and hence the original size is retained. 

Even though cleavage meaning in science simply refers to cell division, a prominent example is a cleavage of the zygote as here one cell gets divided into different part not for reproduction but for the purpose of specialisation as each divided cell grows into a specific type of cell that in turn produce cells that perform a specific function. For example hematopoietic stem cells. 

A prime example of mitosis is the cell cycle of the normal cells of the body dividing for the process of regeneration and in some cases for the process of reproduction. The two daughter cells are identical to the parent cells and do not form a lineage of cells. 

Cleavage of the zygote takes place only in animal cells. 

Takes place in any type of cell whether a plant or an animal cell. 

It is a short phase and it does not involve any growth of the blastomeres (or the divided zygote)

It is a complete long process of nuclear and cytoplasmic division. Also, involves the growth of the daughter cells. 

The overall mass of the cells that have been cleaved will remain the same but the mass of the single divided cell will decrease. 

The mass of the cells will remain the same i.e. equal to each other and each one will be of the same mass as that of the parent cell. 

As the cells get cleaved the nuclear content will increase as compared to cytoplasmic content as the cytoplasmic content gets divided between the cells. 

Overall, the ratio of the nuclear content to that of the cytoplasmic content will remain the same. 

New DNA is synthesized rapidly for the new blastomeres. 

The synthesis of the new DNA takes place at a normal pace as compared to the process of cleavage. 

It is known as cytokinesis and as known mostly occurs in animal cells. 

Mitosis involves two steps: karyokinesis (nuclear division) and cytokinesis (cytoplasmic division).

Actin and myosin filaments forming the contractile ring are the key components of cytokinesis.

Along with the involvement of actin and myosin filaments for cytoplasmic division, spindle fibres made up of microtubules play a key role in nuclear division.

As mentioned above, cleavage differs from mitosis in lacking nuclear division, cytoplasmic division results in two daughter cells with two daughter nuclei each carrying a single one. 

By mitosis definition, it is clear that the nuclear division takes place and the daughter nuclei are created first before the event of cytokinesis.

FAQs (Frequently Asked Questions)

1. What is a Cleavage in the Cell Division?

Ans: A term more prominently related to developmental biology, ‘cleavage’ is the division of the cells in the early embryo. The zygote formed after the fertilisation of the egg with the sperm divides numerous times or is cleaved giving rise to blastomeres which further progress to form the embryo.

2. What is the Difference Between Cleavage and Mitosis?

Ans: Cleavage and mitosis are two events associated with the cell cycle. Whereas cleavage is simply the division of the cytoplasm into two daughter cells, it is the second part of the entire process of mitotic cell division. In mitosis, the nuclear division takes place first which is then followed by the cytoplasmic division.