Biology - Cell Division


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Introduction

  • The process of division of parent cell into two or more daughter cells is known as cell division.

  • In early 1880s, Flemming first observed the process of cell division.

Cell Division
  • Following are the three types of cell division −

    • Amitosis

    • Mitosis &

    • Meiosis

  • Let’s discuss each of them in brief −

Amitosis

  • Parent cell gets divided into two parts, and each of them grows as a new complete organism.

  • Amitosis can be seen in less developed organisms. E.g. bacteria

  • Amitosis is also known as binary fission.

  • There is no stage of division, cell directly gets divided into two new organisms.

Mitosis

  • The process of division of parent cell into two new identical cells is known as mitosis.

  • In both the new cells, the number of chromosomes remain same.

  • Mitosis (cell division) occurs only in eukaryotic cells.

  • In mitosis, the division of the nucleus is preceded by the S stage (i.e. interphase - during this phase, the DNA is replicated).

  • After the interphase, the cytokinesis process begins, which divides the cytoplasm, cell organelles, and cell membrane into two new cells.

  • The process of mitosis is divided into the following stages −

    • Prophase

    • Prometaphase

    • Metaphase

    • Anaphase

    • Telophase

  • The stages of mitosis are described in the following image −

Mitosis
  • Let’s discuss each of them in brief −

Prophase

  • During the prophase, cell prepares to get divided.

  • The prophase process is also known as chromosome condensation, as chromatin fibers condense into discrete chromosomes.

  • Each chromosome has two chromatids and these two chromatids are joined at a place known as centromere.

Prometaphase

  • In this phase, the nuclear envelope gets disintegrated into small membrane vesicles.

Metaphase

  • In this phase, the two centrosomes start pulling the chromosomes towards opposite ends of the cell and ensure the equitable distribution of chromosomes.

Anaphase

  • In this phase two identical daughter chromosomes are formed.

Telophase

  • Telo is a Greek word meaning ‘end’.

  • In this phase, the nuclear envelop gets broken and a new nuclear envelop forms.

  • The new envelope gets formed around each set of separated daughter chromosomes; parallel, the nucleolus reappears.

  • Likewise, the mitosis is complete.

Cytokinesis

  • Cytokinesis, technically, is not a phase of mitosis, but rather a distinct process, essential for completing the cell division.

  • In this phase, cytoplasm begins to divide and completed with the development of two new identical cells.

Meiosis

  • Meiosis is a typical type of cell division in which the chromosome number gets reduced by half, creating four haploid cells. Each cell is genetically distinct from the parent cell.

  • Meiosis cell division process occurs in all sexually reproducing single-celled and multicellular eukaryotes, including plants, animals, and fungi.

Meiosis
  • Meiosis cell division is primarily categorized as Meiosis I and Meiosis II.



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