2. Introduction
Cell Division
Growth and reproduction are characteristic of cells. Indeed of all living organisms. All cell reproduce by dividing
into two, with each parental cell giving rise to two daughter cells each time they divided. These newly formed
daughter cells can be themselves grow and divide, giving rise to a new cell population that is formed by the
growth and division of a single parental cell and its progeny. In other words, such cycle of growth and division
allow a single cell to form a structure consisting of millions of cells.
Rudolf Virchow- proposed the cell lineage theory. Cell lineage theory states “omnis cellula e cellula “i.e. cell
arise from pre-existing cells. Rudolf Virchow failed to prove the theory.
Starsburger -New nuclei arise by division of pre-existing nuclei .
3. Types of Cell division
A. Amitosis or Direct division
B. Mitosis or Indirect cell division
C. Meiosis or Reduction cell division
A. Amitosis
Name Amitosis was given by remake and detail of amitosis is given by Flemming.
It is most primitive type of the cell division.
Chromosome are not visible during division.
It is process of division without recognizable chromosome.
Amitosis does not involve the formation of spindle.
Division of nucleus is direct.
In amitosis division may be equal and unequal.
Amitosis is fastest cell division which may complete in 20 - 30 minute.
4. Division of cytoplasm and nucleus occur simultaneously by the constriction.
Amitosis cell division of prokaryotes. But exceptionally also occurs in some eukaryotes.
eg. Yeast- budding occurs by a mitosis.
In Amoeba Multiple Fission occurs by amitosis .
In Paramecium division of mega nucleus.
In mammals growth of fetal membrane (amnion, chorion, allantois & yolksac).
Division of Mitochondria and chloroplasts.
5. B. Mitosis
It is also known as equational cell division as the two daughter cells formed have the same number of
chromosome as that of the parent cell.
Term mitosis was given by Flemming.
Mitosis occurs in somatic cells. eg.(skin cell, bone marrow cells )
Mitosis is completed in phases-Karyokinesis or nuclear division and Cytokinesis or cytoplasmic division.
Karyokinesis-it comprises of 4 phases
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis- Cytokinesis involves division of cytoplasm and organelles.
It take place in animal and plant cells.
6. C. Meiosis
The term Meiosis was proposed by farmer and Moore.
The specialized kind to cell division that reduced the chromosome number by half results in the
production of haploid daughter cells. This kind of division is called meiosis.
Meiosis ensures the production of applied phase in the life cycle of sexually reproducing organisms
whereas fertilization restores the diploid phase.
In Meiosis during gametogenesis in plant and animals, leads to the formation of haploid gametes.
Gametes are formed specialized diploid cells.
Meiosis involves two sequential cycles of nuclear and cell division called meiosis I and meiosis II
but only a single cycle of DNA replication.
