Cell Division (NCERT) - Class 11 PDF Download

 Page 1


Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009 48
CELL DIVISION
CELL DIVISION
 4 INTRODUCTION 
? W.Flemming at first studied mitotic division in Salamander.
? Strasburger discovered meiosis.
? Strasburger gave name prophase, metaphase, anaphase, telophase.
? Meiosis name was given by Farmer and Moore.
? It is important for development, regeneration and reproduction.
? Hormone cytokinin increases rate of cell division.
 4 TYPES OF DIVISION 
? Amitosis
? Mitosis
? Meiosis
? Amitosis (No spindle, No chromosome)
? It is the simplest mode of cell division at first described by REMAK (1841).
? This type of division starts with elongation of nucleus.
? Nucleus becomes dumbbell shaped, and get divided into two daughter nucleus.
? Nucleur division is followed by the division of cytoplasm its results in formation of two daughter cells.
? In this division, no spindle formation and no distinct chromosome formation occurs. Nuclear evelope remains
intact. The daughter cells are approximately the two equal halves of a parental cell.
e.g. PPLO, Blue-green algae, Bacteria and Eukaryotic cells. Examples are yeast-budding occurs by amitosis.
? Ameoba multiple fission occurs by amitosis.
? Paramecium division of meganucleus.
? Mammals-growth of foetal membranes (amnion, chorion, allantois, yolk sac)
? Division of mitochondria and chloroplasts.
Page 2


Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009 48
CELL DIVISION
CELL DIVISION
 4 INTRODUCTION 
? W.Flemming at first studied mitotic division in Salamander.
? Strasburger discovered meiosis.
? Strasburger gave name prophase, metaphase, anaphase, telophase.
? Meiosis name was given by Farmer and Moore.
? It is important for development, regeneration and reproduction.
? Hormone cytokinin increases rate of cell division.
 4 TYPES OF DIVISION 
? Amitosis
? Mitosis
? Meiosis
? Amitosis (No spindle, No chromosome)
? It is the simplest mode of cell division at first described by REMAK (1841).
? This type of division starts with elongation of nucleus.
? Nucleus becomes dumbbell shaped, and get divided into two daughter nucleus.
? Nucleur division is followed by the division of cytoplasm its results in formation of two daughter cells.
? In this division, no spindle formation and no distinct chromosome formation occurs. Nuclear evelope remains
intact. The daughter cells are approximately the two equal halves of a parental cell.
e.g. PPLO, Blue-green algae, Bacteria and Eukaryotic cells. Examples are yeast-budding occurs by amitosis.
? Ameoba multiple fission occurs by amitosis.
? Paramecium division of meganucleus.
? Mammals-growth of foetal membranes (amnion, chorion, allantois, yolk sac)
? Division of mitochondria and chloroplasts.
Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009
50
 4 MITOSIS 
? Mitosis was discovered by Flemming in 1879 in animal cell  and in plants cells by Strasburger in 1875.
? Mitosis is a cell division in which parent cell divide to form two daughter cell, in which number of chromosome,
amount of DNA, number and types of gene are equal to parent cell.
? It occurs in somatic cell (n, 2n, polyploid any).
? It is called indirect division.
? Mitosis results in increase in number of cells in the body.
Mitosis cell division can be divided into two phases.
G Interphase G Division phase or M phase
? Interphase / Cell cycle
? Interphase is phase between two cell division. group into three sub stages G
1 
S and G
2
.
? In this phase cell prepares itself for division so, called preparatory phase.
? It is longest phase of cell cycle. It get completed approx. in 19-22 hours.
? It is also called resting phase. (previously)
? In this phase, cell remain metabolically extremely active.
? In this phase synthesis of protein, enzyme, DNA and RNA takes place
? Centrosome (Centriole) duplicates into two. Thus two centrosome (4 centriole) are formed.
? Cell cycle can remain arrested only G
1
 phase. Then G
1
 is called as G
0
 phase. G
0
 phase found in cells
of permanent tissue.
? Cell cycle is running by a group of special proteins “Cyclins and Cdks (MPF), (Nurse, T-Hunt &  Hartmann
2001 studies on sacchromyces (Baker yeast))
? Three sub stages of interphase :
? G
1
 phase [6-15 hr] - Most variable phase for duration.
? Cell growth occurs in this phase, so most probably it is longest stage of interphase.
? Mitochondria, Chloroplasts (plants), Lysosomes, Ribosome, Endoplasmic Reticulum Golgi Complex, Vacuoles
etc. are produced.
? Structural and functional proteins are formed.
? Nucleolus produces rRNA, mRNA and tRNA. (RNA synthesis may inhibited by actinomycin).
Page 3


Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009 48
CELL DIVISION
CELL DIVISION
 4 INTRODUCTION 
? W.Flemming at first studied mitotic division in Salamander.
? Strasburger discovered meiosis.
? Strasburger gave name prophase, metaphase, anaphase, telophase.
? Meiosis name was given by Farmer and Moore.
? It is important for development, regeneration and reproduction.
? Hormone cytokinin increases rate of cell division.
 4 TYPES OF DIVISION 
? Amitosis
? Mitosis
? Meiosis
? Amitosis (No spindle, No chromosome)
? It is the simplest mode of cell division at first described by REMAK (1841).
? This type of division starts with elongation of nucleus.
? Nucleus becomes dumbbell shaped, and get divided into two daughter nucleus.
? Nucleur division is followed by the division of cytoplasm its results in formation of two daughter cells.
? In this division, no spindle formation and no distinct chromosome formation occurs. Nuclear evelope remains
intact. The daughter cells are approximately the two equal halves of a parental cell.
e.g. PPLO, Blue-green algae, Bacteria and Eukaryotic cells. Examples are yeast-budding occurs by amitosis.
? Ameoba multiple fission occurs by amitosis.
? Paramecium division of meganucleus.
? Mammals-growth of foetal membranes (amnion, chorion, allantois, yolk sac)
? Division of mitochondria and chloroplasts.
Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009
50
 4 MITOSIS 
? Mitosis was discovered by Flemming in 1879 in animal cell  and in plants cells by Strasburger in 1875.
? Mitosis is a cell division in which parent cell divide to form two daughter cell, in which number of chromosome,
amount of DNA, number and types of gene are equal to parent cell.
? It occurs in somatic cell (n, 2n, polyploid any).
? It is called indirect division.
? Mitosis results in increase in number of cells in the body.
Mitosis cell division can be divided into two phases.
G Interphase G Division phase or M phase
? Interphase / Cell cycle
? Interphase is phase between two cell division. group into three sub stages G
1 
S and G
2
.
? In this phase cell prepares itself for division so, called preparatory phase.
? It is longest phase of cell cycle. It get completed approx. in 19-22 hours.
? It is also called resting phase. (previously)
? In this phase, cell remain metabolically extremely active.
? In this phase synthesis of protein, enzyme, DNA and RNA takes place
? Centrosome (Centriole) duplicates into two. Thus two centrosome (4 centriole) are formed.
? Cell cycle can remain arrested only G
1
 phase. Then G
1
 is called as G
0
 phase. G
0
 phase found in cells
of permanent tissue.
? Cell cycle is running by a group of special proteins “Cyclins and Cdks (MPF), (Nurse, T-Hunt &  Hartmann
2001 studies on sacchromyces (Baker yeast))
? Three sub stages of interphase :
? G
1
 phase [6-15 hr] - Most variable phase for duration.
? Cell growth occurs in this phase, so most probably it is longest stage of interphase.
? Mitochondria, Chloroplasts (plants), Lysosomes, Ribosome, Endoplasmic Reticulum Golgi Complex, Vacuoles
etc. are produced.
? Structural and functional proteins are formed.
? Nucleolus produces rRNA, mRNA and tRNA. (RNA synthesis may inhibited by actinomycin).
Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009 50
? Metabolic rate of the cell becomes very high.
? It may be called pre DNA synthesis phase.
? S-phase [6-10 hr)- (Longest phase in human interphase)
? Replication of DNA takes place. (DNA get doubled)
? Protein molecules called histones are synthesized that cover each strand of DNA.
? Centrosome (Centriole) replicate is late S-phase
? G
2
-phase [3 - 12 hr]
? Tubulin protein synthesis start for spindle formation.
? This phase may be called post DNA synthesis phase.
? Cell division involves enormous expenditure of energy thus cell stores ATP in G
2
 phase
? After G
2
 phase cell enters in division or M-phase
 4 CAUSE OF MITOSIS 
? Kern plasm theory : Hertwig, says that mitosis occurs due to disturbance in karyoplasmic index (KI)
of cell.
n c
n
V V
V
K I
?
?
Here V
n
 = Volume of nucleus
V
c
 = Volume of cell
V
c
 – V
n
 = Volume of cytoplasm
c y t op l a s m o f V ol um e
1
K I ?
Small cell ? less cytoplasm ? High KI ? No division it show nucleus control the activity of
cytoplasm and no division occur.
Large cell ? More cytoplasm ? Low KI ? Division occur. It cause to loose control of nucleus on
cytoplasmic metabolism so large cell divide into two
? Surface area volume Ratio : It says that when cell grows in size its volume increases but surface
area remain less so it affect metabolic activity of cell which result into division of cell.
? Note : Above two hypothesis regarding the division of cell are completely discarded because new
concept give the genetic control of cell division.
 4 CELL DIVISION CONTROL 
? A cell reproduces by performing an orderly set sequences of irreversible events, In which it duplicates
It’s contents & then divides into two, these events are known as cell cycle.
Page 4


Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009 48
CELL DIVISION
CELL DIVISION
 4 INTRODUCTION 
? W.Flemming at first studied mitotic division in Salamander.
? Strasburger discovered meiosis.
? Strasburger gave name prophase, metaphase, anaphase, telophase.
? Meiosis name was given by Farmer and Moore.
? It is important for development, regeneration and reproduction.
? Hormone cytokinin increases rate of cell division.
 4 TYPES OF DIVISION 
? Amitosis
? Mitosis
? Meiosis
? Amitosis (No spindle, No chromosome)
? It is the simplest mode of cell division at first described by REMAK (1841).
? This type of division starts with elongation of nucleus.
? Nucleus becomes dumbbell shaped, and get divided into two daughter nucleus.
? Nucleur division is followed by the division of cytoplasm its results in formation of two daughter cells.
? In this division, no spindle formation and no distinct chromosome formation occurs. Nuclear evelope remains
intact. The daughter cells are approximately the two equal halves of a parental cell.
e.g. PPLO, Blue-green algae, Bacteria and Eukaryotic cells. Examples are yeast-budding occurs by amitosis.
? Ameoba multiple fission occurs by amitosis.
? Paramecium division of meganucleus.
? Mammals-growth of foetal membranes (amnion, chorion, allantois, yolk sac)
? Division of mitochondria and chloroplasts.
Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009
50
 4 MITOSIS 
? Mitosis was discovered by Flemming in 1879 in animal cell  and in plants cells by Strasburger in 1875.
? Mitosis is a cell division in which parent cell divide to form two daughter cell, in which number of chromosome,
amount of DNA, number and types of gene are equal to parent cell.
? It occurs in somatic cell (n, 2n, polyploid any).
? It is called indirect division.
? Mitosis results in increase in number of cells in the body.
Mitosis cell division can be divided into two phases.
G Interphase G Division phase or M phase
? Interphase / Cell cycle
? Interphase is phase between two cell division. group into three sub stages G
1 
S and G
2
.
? In this phase cell prepares itself for division so, called preparatory phase.
? It is longest phase of cell cycle. It get completed approx. in 19-22 hours.
? It is also called resting phase. (previously)
? In this phase, cell remain metabolically extremely active.
? In this phase synthesis of protein, enzyme, DNA and RNA takes place
? Centrosome (Centriole) duplicates into two. Thus two centrosome (4 centriole) are formed.
? Cell cycle can remain arrested only G
1
 phase. Then G
1
 is called as G
0
 phase. G
0
 phase found in cells
of permanent tissue.
? Cell cycle is running by a group of special proteins “Cyclins and Cdks (MPF), (Nurse, T-Hunt &  Hartmann
2001 studies on sacchromyces (Baker yeast))
? Three sub stages of interphase :
? G
1
 phase [6-15 hr] - Most variable phase for duration.
? Cell growth occurs in this phase, so most probably it is longest stage of interphase.
? Mitochondria, Chloroplasts (plants), Lysosomes, Ribosome, Endoplasmic Reticulum Golgi Complex, Vacuoles
etc. are produced.
? Structural and functional proteins are formed.
? Nucleolus produces rRNA, mRNA and tRNA. (RNA synthesis may inhibited by actinomycin).
Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009 50
? Metabolic rate of the cell becomes very high.
? It may be called pre DNA synthesis phase.
? S-phase [6-10 hr)- (Longest phase in human interphase)
? Replication of DNA takes place. (DNA get doubled)
? Protein molecules called histones are synthesized that cover each strand of DNA.
? Centrosome (Centriole) replicate is late S-phase
? G
2
-phase [3 - 12 hr]
? Tubulin protein synthesis start for spindle formation.
? This phase may be called post DNA synthesis phase.
? Cell division involves enormous expenditure of energy thus cell stores ATP in G
2
 phase
? After G
2
 phase cell enters in division or M-phase
 4 CAUSE OF MITOSIS 
? Kern plasm theory : Hertwig, says that mitosis occurs due to disturbance in karyoplasmic index (KI)
of cell.
n c
n
V V
V
K I
?
?
Here V
n
 = Volume of nucleus
V
c
 = Volume of cell
V
c
 – V
n
 = Volume of cytoplasm
c y t op l a s m o f V ol um e
1
K I ?
Small cell ? less cytoplasm ? High KI ? No division it show nucleus control the activity of
cytoplasm and no division occur.
Large cell ? More cytoplasm ? Low KI ? Division occur. It cause to loose control of nucleus on
cytoplasmic metabolism so large cell divide into two
? Surface area volume Ratio : It says that when cell grows in size its volume increases but surface
area remain less so it affect metabolic activity of cell which result into division of cell.
? Note : Above two hypothesis regarding the division of cell are completely discarded because new
concept give the genetic control of cell division.
 4 CELL DIVISION CONTROL 
? A cell reproduces by performing an orderly set sequences of irreversible events, In which it duplicates
It’s contents & then divides into two, these events are known as cell cycle.
Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009
52
G
1
S
G
2
M
Mitosis promoting factor
M-Cdk 
?
M-cyclin
Cdk
S-Cdk
DNA replication promoting factor
?
S-cyclin
G
2
S
Cdk 
Degenerating 
M-cyclin
Degenerating 
S-cyclin
? Molecular biologists, identifying the biomolecules, that control or drive the cell cycle, many biologists, some of
whom worked with invertebrate or frog egg’s others with yeast cell or cell culture.
? Scientists concluded that the activity of enzymes, known as cyclin dependant kinases. (Cdk’s) regulates the
cell cycle.
? They are activated when they combined with key protein called cyclin.
? Kinase is an enzyme that removes a phosphate group from ATP & add to another protein.
? At some check points ?
?
?
?
?
?
?
?
?
?
M G
S G
2
1
 a kinase enzyme combines with cyclin & this moves the cell cycle forwardly.
? S-kinase is capable of starting the replication of DNA after it combined with S-cyclin (G
1
 - Cyclin). After some
time S-cyclin is destroyed & S-kinase is no longer active.
? M-kinase is capable of turning on mitosis after it has bind with M-cyclin, (G
2
-cyclin).
? The detail of cell cycle varied from organism to organism & different time in an organism. However certain
characteristics are universal component of cell cycle control.
Genes
CDC2, CDC28-designated in Budding yeast
cdc2, cdc-28, designated in fission yeast
? Division Phase
In this phase nuclear and cytoplasmic division takes place.
Karyokinesis- Nuclear division.
Cytokinesis-Cytoplasmic division.
Page 5


Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009 48
CELL DIVISION
CELL DIVISION
 4 INTRODUCTION 
? W.Flemming at first studied mitotic division in Salamander.
? Strasburger discovered meiosis.
? Strasburger gave name prophase, metaphase, anaphase, telophase.
? Meiosis name was given by Farmer and Moore.
? It is important for development, regeneration and reproduction.
? Hormone cytokinin increases rate of cell division.
 4 TYPES OF DIVISION 
? Amitosis
? Mitosis
? Meiosis
? Amitosis (No spindle, No chromosome)
? It is the simplest mode of cell division at first described by REMAK (1841).
? This type of division starts with elongation of nucleus.
? Nucleus becomes dumbbell shaped, and get divided into two daughter nucleus.
? Nucleur division is followed by the division of cytoplasm its results in formation of two daughter cells.
? In this division, no spindle formation and no distinct chromosome formation occurs. Nuclear evelope remains
intact. The daughter cells are approximately the two equal halves of a parental cell.
e.g. PPLO, Blue-green algae, Bacteria and Eukaryotic cells. Examples are yeast-budding occurs by amitosis.
? Ameoba multiple fission occurs by amitosis.
? Paramecium division of meganucleus.
? Mammals-growth of foetal membranes (amnion, chorion, allantois, yolk sac)
? Division of mitochondria and chloroplasts.
Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009
50
 4 MITOSIS 
? Mitosis was discovered by Flemming in 1879 in animal cell  and in plants cells by Strasburger in 1875.
? Mitosis is a cell division in which parent cell divide to form two daughter cell, in which number of chromosome,
amount of DNA, number and types of gene are equal to parent cell.
? It occurs in somatic cell (n, 2n, polyploid any).
? It is called indirect division.
? Mitosis results in increase in number of cells in the body.
Mitosis cell division can be divided into two phases.
G Interphase G Division phase or M phase
? Interphase / Cell cycle
? Interphase is phase between two cell division. group into three sub stages G
1 
S and G
2
.
? In this phase cell prepares itself for division so, called preparatory phase.
? It is longest phase of cell cycle. It get completed approx. in 19-22 hours.
? It is also called resting phase. (previously)
? In this phase, cell remain metabolically extremely active.
? In this phase synthesis of protein, enzyme, DNA and RNA takes place
? Centrosome (Centriole) duplicates into two. Thus two centrosome (4 centriole) are formed.
? Cell cycle can remain arrested only G
1
 phase. Then G
1
 is called as G
0
 phase. G
0
 phase found in cells
of permanent tissue.
? Cell cycle is running by a group of special proteins “Cyclins and Cdks (MPF), (Nurse, T-Hunt &  Hartmann
2001 studies on sacchromyces (Baker yeast))
? Three sub stages of interphase :
? G
1
 phase [6-15 hr] - Most variable phase for duration.
? Cell growth occurs in this phase, so most probably it is longest stage of interphase.
? Mitochondria, Chloroplasts (plants), Lysosomes, Ribosome, Endoplasmic Reticulum Golgi Complex, Vacuoles
etc. are produced.
? Structural and functional proteins are formed.
? Nucleolus produces rRNA, mRNA and tRNA. (RNA synthesis may inhibited by actinomycin).
Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009 50
? Metabolic rate of the cell becomes very high.
? It may be called pre DNA synthesis phase.
? S-phase [6-10 hr)- (Longest phase in human interphase)
? Replication of DNA takes place. (DNA get doubled)
? Protein molecules called histones are synthesized that cover each strand of DNA.
? Centrosome (Centriole) replicate is late S-phase
? G
2
-phase [3 - 12 hr]
? Tubulin protein synthesis start for spindle formation.
? This phase may be called post DNA synthesis phase.
? Cell division involves enormous expenditure of energy thus cell stores ATP in G
2
 phase
? After G
2
 phase cell enters in division or M-phase
 4 CAUSE OF MITOSIS 
? Kern plasm theory : Hertwig, says that mitosis occurs due to disturbance in karyoplasmic index (KI)
of cell.
n c
n
V V
V
K I
?
?
Here V
n
 = Volume of nucleus
V
c
 = Volume of cell
V
c
 – V
n
 = Volume of cytoplasm
c y t op l a s m o f V ol um e
1
K I ?
Small cell ? less cytoplasm ? High KI ? No division it show nucleus control the activity of
cytoplasm and no division occur.
Large cell ? More cytoplasm ? Low KI ? Division occur. It cause to loose control of nucleus on
cytoplasmic metabolism so large cell divide into two
? Surface area volume Ratio : It says that when cell grows in size its volume increases but surface
area remain less so it affect metabolic activity of cell which result into division of cell.
? Note : Above two hypothesis regarding the division of cell are completely discarded because new
concept give the genetic control of cell division.
 4 CELL DIVISION CONTROL 
? A cell reproduces by performing an orderly set sequences of irreversible events, In which it duplicates
It’s contents & then divides into two, these events are known as cell cycle.
Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009
52
G
1
S
G
2
M
Mitosis promoting factor
M-Cdk 
?
M-cyclin
Cdk
S-Cdk
DNA replication promoting factor
?
S-cyclin
G
2
S
Cdk 
Degenerating 
M-cyclin
Degenerating 
S-cyclin
? Molecular biologists, identifying the biomolecules, that control or drive the cell cycle, many biologists, some of
whom worked with invertebrate or frog egg’s others with yeast cell or cell culture.
? Scientists concluded that the activity of enzymes, known as cyclin dependant kinases. (Cdk’s) regulates the
cell cycle.
? They are activated when they combined with key protein called cyclin.
? Kinase is an enzyme that removes a phosphate group from ATP & add to another protein.
? At some check points ?
?
?
?
?
?
?
?
?
?
M G
S G
2
1
 a kinase enzyme combines with cyclin & this moves the cell cycle forwardly.
? S-kinase is capable of starting the replication of DNA after it combined with S-cyclin (G
1
 - Cyclin). After some
time S-cyclin is destroyed & S-kinase is no longer active.
? M-kinase is capable of turning on mitosis after it has bind with M-cyclin, (G
2
-cyclin).
? The detail of cell cycle varied from organism to organism & different time in an organism. However certain
characteristics are universal component of cell cycle control.
Genes
CDC2, CDC28-designated in Budding yeast
cdc2, cdc-28, designated in fission yeast
? Division Phase
In this phase nuclear and cytoplasmic division takes place.
Karyokinesis- Nuclear division.
Cytokinesis-Cytoplasmic division.
Cell Division – Nirmaan TYCRP
 97/1, 3F, Adhchini, Sri Aurobindo Marg, Near NCERT, New Delhi |  011-32044009 52
? Karyokinesis
It is divided into four phases –
G Prophase G Metaphase G Anaphase G Telophase
? Prophase
? It is the longest phase of karyokinesis.
? Chromosomes appear as pairs of chromatids joined by centromere (chromatin condensation start).
? The nuclear membrane disintegrate and disappear into the cytoplasm.
? Nucleolus start disappearing.
? Each centrioles Separates and start to move towards the opposite pole of the cell.
? Around each centriole astral rays are formed in the cytoplasm. due to (gelation of protein).
? Anastral mitosis - In plants, centrioles are absent and no asters are formed. Mitosis without asters is known
as anastral mitosis.
? Amphiastral Mitosis - In animals, the asters are present and the mitosis is described as amphiastral, or astral
mitosis.
? Metaphase
? The chromosome arrange at the equatorial plane.
? Each centromere is joined by two chromosomal fibre or kinetochore spindle one from each pole.
? Some other fibres of the spindle extend from one pole to the other pole. These are known as continous fibres or non
kinetochore spindle
? Centromere lies at equator and arms remain directed towards poles.
? Chromosomal fibre have polarity i.e. + end at equator and – end at the pole.
? In metaphase each chromosome splits lengthwise upto the centromere (division of matrix of chromosome).
Thus replicated chromatids clearly visible at metaphase stage.
? Anaphase (Smallest stage)
? The fibres which occur in  between the chromosomes are called interzonal/non kinetochore spindle fibres.
? In early anaphase interzonal fibres (small and contracted) appears at equator of cell.
? Centromere of each chromosome splits lengthwise (division of centromere).
? Number of chromosome becomes double in cell during mitotic anaphase.
? Interzonal fibres expands and they push chromosomes towards the oppsite poles.(Pushing)
? Chromosomal fibres contract and they pull chromosome towards opposite poles. (Pulling)
? By pulling and pushing mechanism chromosomes rapidily move towards the opposite poles.
? Approximately 30 ATP are required to carry a chromosome to pole. Chromosomes reach at poles in late
anaphase.
? At this phase cytokinesis process starts.
? Telophase (Reverse prophase)
? The daughter chromosomes with their centromere at the poles begin to uncoil and lengthen. They aggregate
together to form a mass at the poles.
? The nucleolus reappear.
? New nuclear membrane develops around the chromosomes from the elements of the E.R.
? Spindle and astral fibre are absorbed in the cytoplasm.
? Thus two daughter nuclei are formed and they have the appearance of the interphase nuclei.