Cell division stages: mitosis & meiosis

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cell division

There are three types of cell division stages.

Amitosis: Division of the total cell along with nucleus.

Mitosis: Vegetative method of division, two identical cells produced.

Meiosis: This cell division stages are also known as the Reduction division, reproductive method of division, four haploid cells produced.

Cell cycle

The cell cycle is observed in mitosis and meiosis. The cell cycle is the period between a cell and a cell division in the production of two daughter cells. The cell cycle consists of interface, division of the nucleus or mitotic phase (phase m) and cytokinesis (phase c)

Interface
It is the longest period of the cell cycle, that is, 90 to 95% of the total cell cycle. It is further divided into G, phase (gap I), S phase (synthetic) and phase G2 (gap 2)

G1
This stage is characterized by the production of essential RNA and proteins and an increase in cell volume.

S.
Phase S is followed im

G2
. The final stage of protein and RNA synthesis occurs. Energy-rich compounds are produced.

cell cycle fig.
cell cycle

 II. Mitotic phase.

The mitotic phase constitutes 05 to 10% of the cell cycle time. Duplicated chromosomes separate; two chromosomal groups are produced and finally two nuclei are produced. Ately DNA replication and duplication are carried out.

III. Cytokinesis.

Go to phase M immediately. The cytoplasm divides into two daughter cells

Amitosis
In this type of cell division stages the cell division shows direct division of the nucleus followed by cytoplasm. It is seen in a lower group of animals such as protozoa and fetal membrane cells. first the By stretching the nucleus, a constriction appears in the nucleus. The nucleus divides into EW. Simultaneously the cytoplasm divides. Two cells are produced.

Mitosis
Mitosis cell division stages also known as somatic cell division or equitable division. In the cell division stages of mitosis, nuclear division or karyokinesis is followed by cytokinesis. Cariokinesis progresses through 4 stages.

(i) Prophase.

(a)Chromatin fiber condensation on chromosomes.
(b) The chromatids are held together by a centromere.
(c) The disappearance of the nucleolus and nuclear membrane.

(ii) Metaphase.

(a) Chromosomes are more condensed and different.

(b) The spindle fibers are joined with centromeres.

(c) Arrangement of chromosomes on the equatorial plate.

(iii) Anaphase.

  • (a) The division of the centromere is carried out.
  • (b) Two chromosomes are produced.
  • (c) The movement of the individual chromosome begins at opposite poles.

(iv) Telophase.

  • (a) The congregation of chromosomes is located at two opposite poles of the cell.
  • (b) The reorganization of the nucleolus and the nuclear membrane is completed.
  • (c) Two nuclei are finally organized.

(v) Cytokinesis.

  • (a) Nuclear separation is simultaneously followed by the division of the cytoplasm.
  • (b) The middle lamina appears in the center of the cell. IT GU
  • (c) Two cells are produced

Meaning.

  • Genetic balance is maintained between different generations.
  • Aids in organ growth, repairs injuries. 0 or lie
  • It is useful in asexual reproduction in lower organisms.
stages of mitosis
cycle of mitosis

Meiosis

This is another type of cell division stage. Meiosis, also called reduction division .tMeiosis takes place in reproductive cells. It is a kind of division where chromosomes number is reduced to half. Four haploid cells are produced from a diploid cell. Meiosis is completed by two types of nuclear divisions. Meiosis I or reduction division and meiosis II or mitotic division.

 Meiosis I

It passes through prophase I, metaphase I, anaphase I and telophase I.

 Prophase I

It is a very long complex phase. The reduction of chromosome passes through certain substages.

 (a) Leptotene. Chromosomes appear as long, thread-like structures.

(b) Zygotene. The pairing between homologous chromosomes takes place. It is called synapse Bivalents are produced.

(c) Pachytene. Crossing over between non-sister chromatids.

(d) Diplotene. Chiasmata formation is seen at point separation of homologs. € Diakinesis. Condensation of chromosomes, criminalization, and disappearance of the nucleolus and nuclear membrane.

Metaphase I

  • Arrangement of homologous chromosomes at equatorial plate.
  • Attachment of spindle fibers with each homologous pair. Anaphase I. Movement of chromosomes towards opposite poles.

Telophase I.

Chromosomes at opposite poles reorganize, nucleolus and nuclear membrane reappear. Meiosis II. It is mitosis like division. Significance.

  • Genetic recombination takes place.
  • Variation leads to evolution.
  • Formation of gametes for sexual reproduction and genetic continuity.

Significance of Cell Division stages.

The Cell division stages include amitosis, mitosis, and meiosis.

  1. Mitosis helps in maintaining genetic stability within the population.
  2. Growth of organism, replacement of damaged tissue is carried by mitosis.
  3. Asexual reproduction in many plants and animal species is done by mitosis.
  4. Production of gametes by meiosis helps the organism to multiply their number.
  5. The recombination of genes involves the production of new species.
  6. So, meiosis helps in the evolution process.
  7. Amitosis is useful for asexual reproduction in lower organisms.

cell division stages

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