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.
FAQs on Difference Between Cleavage and Mitosis
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.