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Cell cycle and cell division concept 10


01
 
DEFINITION
Cell cycle
  • Cell cycle is a genetically controlled series of changes that occur in a newly formed cell by which it duplicates its genome, synthesises other constituents, undergoes growth and divides to form two daughter cells.
02
 
DEFINITION
Structure of cell cycle
  • Cell cycle is composed of four phases- Interphase (G1, G2), S phase (synthetic phase), cell division (mitosis/meiosis).
03
 
DEFINITION
Mitosis
  • Mitosis is an equational division, in which one parent cell divides into two identical daughter cells.
04
 
DEFINITION
Significance of mitosis
  • It is responsible for growth and development of multicellular organisms from a single-celled zygote.
  • It repairs the damaged and wounded tissues.
  • It helps in maintaining the same chromosome number in daughter cells.
05
 
DEFINITION
Karyokinesis
  • All the nuclear changes that occur during the cell division are collectively termed as karyokinesis.
06
 
DEFINITION
Cytokinesis
  • Cytokinesis is the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells. 
07
 
DEFINITION
Prophase
  • It is the first phase of cell division, during which the chromosomes get condensed and duplicated to produce chromatids.
08
 
DEFINITION
The phases of mitosis
Various phases of mitosis can be observed in the above figure.
09
 
DEFINITION
Mitosis in plant cell and animal cell
The difference between mitosis in plant cell and animal cell are as follows:
Plant cellAnimal cell
Centrioles are absent.Centrioles are present.
No aster formation.Aster formation occurs.
Cell plate is formed.No cell plate is formed.
No furrowing of cytoplasm at cytokinesis.Furrowing of cytoplasm occurs.
Occurs mainly in meristems.Occurs in tissues throughout the body.
10
 
DEFINITION
Plant cytokinesis
Plant cytokinesis is different from animal cytokinesis due to presence of a solid cell wall on the outside. They are of two types:
  • Cleavage method
  • Cell plate method
11
 
DEFINITION
Meiosis
  • Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells.
12
 
DEFINITION
Significance of meiosis
1. It maintains the same chromosome n umber in the sexually reproducing organisms. From a diploid cell, haploid gametes are produced which in turn fuse to form a diploid cell.
2. It restricts the multiplication of chromosome number and maintains the stability of the species.
3. Maternal and paternal genes get exchanged during crossing over. It results in variations among the offspring.
4. All the four chromatids of a homologous pair of chromosomes segregate and go over separately to four different daughter cells. This leads to variation in the daughter cells genetically.
13
 
DEFINITION
Gametic meiosis
  • Gametic meiosis takes place in animals during the formulation of gametes.
  • It results in diplontic life cycle.
14
 
DEFINITION
Zygotic meiosis
  • Zygotic meiosis takes place in lower plants in the zygote and the resulting organisms are haploid.
  • They have haplontic life cycle.
15
 
DEFINITION
Significance of meiosis
  • It maintains the same chromosome number in the sexually reproducing organisms.
  • It provides a way for mixing up of genes, which occurs in two ways: the maternal and paternal chromosomes gets mixed up and cross joining.
16
 
DEFINITION
Significance of meiosis 1/mitosis
1. It is an equational division through which identical daughter cells are produced having the same amount and type of genetic constitution as that of the parent cell.
2. It is responsible for growth and development of multi-cellular organisms from a single-celled zygote.
3. The number of chromosomes remains the same in all the cells produced by this division. Thus, the daughter cells retain the same characters as those of the parent cell.
4. It helps the cell in maintaining proper size.
5. Mitosis helps in restoring wear and tear in body tissues, replacement of damaged or lost part, healing of wounds and regeneration of detached parts (as in tail of a lizards).
6. It is a method of multiplication in unicellular organisms.
7. If mitosis remains unchecked, it may result in uncontrolled growth of cells leading to cancer or tumour.
17
 
DEFINITION
Prophase 1
GIF
  • Chromosomes becomes shorter and thicker, clearly visible in microscope. Nucleus disappears during this phase. It has four phases-
  • Leptotene - The chromosomes condenses and are visible under electron microscope.
  • Zygotene - It is the sub-stage, where synapsis between homologous chromosomes begins.
  • Pachytene - Crossing over starts within the bivalents. The synaptonemal complex is complete, allowing chiasma to form.
  • Diplotene - The synaptonemal complex degrades and homologous chromosomes separate from one another a little.
  • Diakinesis - Chromosomes condense further during the this stage. The four parts of the tetrads are actually visible.
18
 
DEFINITION
Leptotene
  • Leptotene - The chromosomes condenses and are visible under electron microscope.
19
 
DEFINITION
Zygotene
  • Zygotene - It is the sub-stage, where synapsis between homologous chromosomes begins.
20
 
DEFINITION
Pachytene
  • Pachytene - Crossing over starts within the bivalents. The synaptonemal complex is complete, allowing chiasma to form.
21
 
DEFINITION
Diplotene
  • Diplotene - The synaptonemal complex degrades and homologous chromosomes separate from one another a little.
22
 
DEFINITION
Diakinesis
  • Diakinesis - Chromosomes condense further during the this stage. The four parts of the tetrads are actually visible.
23
 
DEFINITION
Metaphase 1
  • Homologous pairs move together along the metaphase plate.
24
 
DEFINITION
Anaphase 1
  • Terminal movement of chromosomes starts.
25
 
DEFINITION
Telophase 1
  • Chromosomes arrived at poles of the cell. Each daughter cell now has half the number of chromosomes but each chromosome consists of a pair of chromatids.
26
 
DEFINITION
Meiosis 2
    1. Phases of Meiosis II
    The second meiotic division is very much similar to mitosis.It has the following steps:

    • Prophase II
      • The events of prophase II are similar to mitotic prophase.
      • Nucleolus and nuclear membrane disappear.
      • Spindle fibres are formed at each pole.
    • Metaphase II
      • Chromosomes move to the centre of the equatorial plane.
      • They get attached to spindle fibres centromere.
    • Anaphase II
      • The sister chromatids separate from one another and are pulled to opposite poles of the spindle due to contraction of the spindle fibres.
    • Telophase II
      • The chromosomes begin to uncoil and become thin.
      • They reorganize into the nucleus with the reappearance of the nucleolus and nuclear membrane in each pole.
      • Cytokinesis follows and four haploid daughter cells are formed and thus the meiotic division is completed.
27
 
DEFINITION
Meiosis and mitosis
The difference between meiosis and mitosis are as follows:
MitosisMeiosis
Occurs in somatic cellsOccurs in reproductive cells
Chromosome or DNA replication is followed by one nuclear division, thereby maintaining the amount of DNA and the number of chromosomes per cell constantly from generation to generationChromosome or DNA replication is followed by two nuclear divisions. Thus, each of the daughter cells contains half as many chromosomes and half as much DNA as its parent cell
Two daughter nuclei are produced from a single parental nucleusFour daughter nuclei are produced from a single parental nucleus
The prophase is comparatively shorter duration and does not have  any subgroupsProphase is a longer duration. It is differentiated into subgroups
All chromosomes behave independently of each otherHomologous chromosomes get paired together
There is no crossing-over or exchange of chromatids between homologous chromosomesCrossing-over or exchange of parts of chromatid between homologous chromosomes is a rule
 

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