Mitosis

Stages of mitosis, Five Stages of mitosis Significance

Stages of mitosis:

Here I shall discuess about the Stages of mitosis, Five Stages of mitosis Significance.  The cell division mitosis is a continuous process. During mitosis, karyokinesis is usually followed by cytokinesis. Karyokinesis and cytokinesis represent the division of nucleus and the division of cytoplasm respectively. Before the starting of the cell division, a cell has to prepare itself. This stage is called interpahse. For the ease of description, the process mitosis can be divided into five stages.

Kinds of Stages of mitosis:

Mitosis

 

(1) Pro-phase

(2) Prometaphase

(3) Metaphase

(4) Anaphase

(5) Telophase

Now lets we see the details:

(a) Prophase:

This is the first stage of mitosis. At the onset of the stage, nucleus becomes little larger and chromatin fibers start condensing into short, thick and tightly coiled structures called chromosomes. At this stage, chromosome can be seen under compound microscope. Though every chromosome then divides into two sister chromatids, at the centromere each one remains together. As the chromosomes are still in a mess from, it is little tough to count the number of chromosome easily in a cell.

 

(b) Prometaphase:

 

At the very early of the stage, spindle apparatus having two poles is developed in plant cells from fiber protein. The middle plane of the spindle apparatus is called equator. Spindle fibers are stretched from one pole to the other. They are called spindle fibers. At this stage kinetochores in centromeres of chromosomes get
attached with some fibers of spindle apparatus.

 

Kinetochores are protein structures assembled on centromeres and link the chromosomes with mitotic spindles. These fibers are generally called traction fibers. They are also called chromosomal fiber as chromosomes are attached with them. Chromosomes then start assembling on the equatorial plane. The nuclear membrane and nucleolus being disintegrated begin to disappear. In animal cells spindle apparatus is developed from centrioles, and the centrioles remain in two poles with astral rays spreading round from them.

 

(c) Metaphase:

 

At the onset of the stage, all the chromosomes complete their assembling at the equator, middle plane from the two poles. The centromere of each chromosome remains on the equator but the two arms take position towards the poles. In this stage, chromosomes look most short and thick. Attraction between chromatids decline and repulsion increases. At the late of the stage, division of centromere starts. Nuclear membrane and nucleolus disappear completely

The significance of mitosis in the living body of organisms is immense. The balance in between the nucleus and cytoplasm of a cell in terms of volume and amount is maintained by the process of cell division mitosis. Through mitosis, the growth in the body multicellular organisms occurs. All the multicellular organisms start their life from a single cell zygote. The repeated division of this single cell produces innumerable cells and thus an organism grows to its complete level. As the number and feature of chromosome remain unchanged in the cells produced through mitosis, growth in organisms takes place systematically. Mitosis plays a role in

 

Mitosis plays a role in the maintenance of normal size, shape and volume of cells. Unicellular organisms reproduce through mitosis. Mitosis plays an important role in the vegetative reproduction of organisms and increasing the number of reproductive cells. Mitosis is essential in the body of living organisms to form new cells continuously for growth and healing of injuries. The life span of some cells is specific and they are, accordingly, replaced through the process of mitosis. As identical cells are produced through mitosis, qualitative features in the living world remain unchanged. Mitotic errors may result in abnormal mass of cells called tumours, with or without cancer cells.

The question is why meiosis occurs. In process mitosis, the number of chromosomes in the daughter cells remains the same as that of their mother cell. Mitosis is essential for the growth and asexual reproduction of organisms.

 

In sexual reproduction, the union of male and female gametes is required. If the number of chromosomes in the reproductive cells would be the same as the vegetative cells, the zygote would contain twice number of chromosomes than that of the vegetative cell. Supposing the number of chromosomes in a vegetative and a reproductive cell of an organism is 4. In zygote the number of chromosome would be 8, and so the new organisms will have the body cells with chromosome number 8 and that is twice that of its mother organism. If every life cycle of an organism continues that way, the number of

 

If every life cycle of an organism continues that way, the number of chromosome would be doubled again and again. In the second chapter, we have learn that chromosomes bear the genes controlling the features of organisms. If the number of chromosome is increased life cycle after life cycle, the offspring will be basically different.

In sexual reproduction, even through the union of male and female gametes, the number of chromosomes remains the same generation after generation as the number of chromosomes becomes half in the reproductive cells than that of the mother cell. When at the time of the development of reproductive cells and in any stage of the life cycle of plants in lower groups, the process meiosis occurs, then the feature of possessing half number of chromosome is called haploid. When the haploid cells are fused, the state of

 

When the haploid cells are fused, the state of cell having two sets of chromosome is called diploid. As the meiosis cell division occurs, the features in the species of living organisms keep on the same more or less, generation after generation. Meiosis mainly occurs in the primordial germinal cells during the development of gametes. In the anthers and ovules of flowering plants, and in the testes and ovaries of animals meiosis occurs. During the development of pollens from diploid pollen mother cells in mosses and ferns, meiosis occurs in their zygotes.

Two consecutive divisions occur with a cell in the process meiosis. The first and the second division are called meiosis-1 and meiosis-II respectively. In the first division meiosis I, the number of chromosome in a daughter cell becomes half than that of its mother cell, and the second division is simply a mitosis. Because of meiosis, the chromosome number in organisms remains constant.

So generation after generation, the number of chromosomes remains the same in the cells of the body of offspring. Besides, genetic diversity is also found in species of organisms as the exchange of genes occurs during meiosis.

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