Cell Division

• Firstly observed by Flemming (in 1882).
• Hence Flemming is known as Father of Cell division.
• According to theory of cell division old cells splits into new cells & formation of new cell is called Cell division.
• This process is also called as Cell production.

• Types of cell division:
• Amitosis
• Mitosis
• Meiosis

• Amitosis:

• This is takes place in less developed (Prokaryotic) cell of unicellular organisms.
• In this division First nucleus of cell is divided and later cytoplasm is divided and two new cells are formed.
• This type of cell division takes place in Bacteria, Blue Green algae, Yeast, Amoeba, Protozoa etc.

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• Mitosis:

• It is also called as somatic cell division.
• In such type of cell division two identical cells are produced.
• In mitosis cell is divide but the number of chromosome remains same and mitosis is a continuous process.
• In mitosis various phases are occurs- Karyokinesis{Prophase, Metaphase, Anaphase, Telophase} & Cytokinesis and cell divides itself stage by stage.

             A) Prophase:

• In animal cell & fungi centriole duplicates itself & move to the opposite end of cell & spindle fiber develop on each centrioles.
• In plant cells spindle fiber develop without presence of centrioles.
• The chromosome which are already duplicated become shorten & thicken.
• Duplicated chromatides of each chromosome held together by centromere.
• The nucleus & nuclear membrane begin to disintegrated in late prophase.

             B) Metaphase:

• Nuclear membrane disappear completly.
• The pairs of chromosome align themselves in such a way that the center of cell and each centromere becomes attached to one spindle fiber from each pole.
• The centromere divides & separate chromatides becomes independent daughter chromosome.

             C) Anaphase: 

• The daughter chromosome move apart from each other & migrate to opposite poles.
• Spindle fiber becomes shorter.

             D) Telophase:

• Daughter chromosome reach the poles, now spindle fiber totally disappear.
• Nuclear membrane forms around each new group of chromosome.    

              E) Cytokinesis:

• After the division of nucleus, the cytoplasm start to divide.
• Cytokinesis is the division of the cell's cytoplasm.
• At the end of cytokinesis, two genetically identical daughter cells are produced.

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• Meiosis:

• The process of meiosis occurs in reproductive cell.
• Thus gametes are produced with half number of chromosome normally found tn body cells.
• Meiosis results in the reduction of number of chromosome in daughter cell by half so it is called as Reduction division.
• This process brings stability in the number of chromosome in an organism, thus haploid gametes fuses & produce diploid zygote.
• It has two stages:

             A) Meiosis I:

• In this stage number of chromosome is reduced to half so the diploid nucleus gives rise to two haploid ones.

              B) Meiosis II:

• In this stage the haploid nuclei divide mitotically to produce four haploid daughter nuclei.

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