mitosis by sukhmani suman

1. Definition: It is also called indirect cell
division or somatic cell division or
equational division.
In this, mature somatic cell divides in such
a way that chromosome number is kept
constant in daughter cell equal to those in
parent cell, so the daughter cells are
quantitatively similar to the parent cell, so
it is called equational division.
DISCOVERY :
It is discovered in animal cells by german
biologist W. Flemming (1882 A.D) . Term
mitosis was given by Flemming(1882 A.D).
Time taken :
It ranges from 30 minutes to 3 hours . Time is
species specific. It also depends upon the type
of tissues, temperature etc.
Occurrence: Mitosis occur in both somatic
cells as well as germ cells of the gonads(
during multiplicative phase of gametogenesis)

2. In Man, it occurs in skin, bone marrow, etc. It
also occurs during embryonic development.
Mitosis occur in both haploid cells as well as
diploid cells.
PHASES OF MITOSIS
 Karyokinesis or Nuclear division
 Cytokinesis or Cytoplasmic division
A. KARYOKINESIS: It comprises four
phases on the basis of position and
morphology of chromosomes.
Explanation
a) Prophase
i. Early prophase
ii. Mid prophase
iii. Late prophase
b) Metaphase
c) Anaphase
d) Telophase
B.CYTOKINESIS
i. In animal cells ( furrowing)

3. ii. In plant cells ( cell plate method)
I. PROPHASE
 It is the phase of longest duration. It is
again of three subphases :
 Early prophase: it is characterized by
formation of asters and condensation of
chromatin
 Formation of asters: It involves:
 Disappearance of centrospheres
 Development and elongation of
microtubules between two centriole pairs
 Centriole pairs (diplosomes) start moving
towards opposite poles.
 Each centriole pair develops fine, radiating
protein-microtubules called astral rays,
forming star- shaped body called aster.
 Condensation of chromatin:
Nuclear chromatin condenses into long,
thin, thread-like chromosomes by
dehydration and spiralization. Each
chromosomes is formed of two sister

4. chromatids joined at centromereOn the
surface of each centromere, there are two
disc like areas called kinetochores, are the
sites of attachment spindlefibers.
II. MID PROPHASE
It is characterized by:
 More condensation of chromosomes, so
that these becomeshorter, thicker and
untangled
 Further moving away of two asters due
to more elongation of microtubules
 Nuclear membrane and nucleolous start
disappearing.

III. Late Prophase
It is characterized by :
 Nearly complete disappearance of Golgi
body, ER,nuclear membrane and nucleolus.
 Further condensation of chromosomes.

5.  Chromosomes move towards the nuclear
membrane leaving a clear crystal area.
 Formation of spindle: Two asters become
antipodal in position and the proteinous
microtubules between them take the form of
spindle. The central broader part of spindle
is called Equator, while narrow ends of
spindle having asters are called poles.
 Spindle is formed of two types of spindle
fibres:
Chromosomal or discontinuous fibres: These
extend frompole to kinetochores of the
chromosomes.
Continous or interpolar fibres: These extend
from pole to pole without coming in contact
with chromosomes.
 Both the asters and the spindle are
collectively called mitotic apparatus.
2. Metaphase (chromosomal orientation at the
equatorial plate)

6. It takes about 2-10 minutes and is
characterized by :
 Each centromere is joined by two
chromosomal fibres, one from each pole.
 Centromeres lie at the equator while arms
are directed towards the poles.
 Mitosis in which the spindle has centrioles
and asters are absent is called anastral and
found in higher plants.
3. ANAPHASE (shortest duration : 2-3
minutes)
At anaphase, the equilibrium of forces that
characterizes
 Metaphase is broken by the sepration of
the kinetochores.
 The kinetochores move apart ,and the
chromatids seprate and begin their
migration toward the poles.
It is characterized by :

7.  Each centromere splits, so that two sister
chromatids have their own centromere and
daughter chromosomes are formed.
 Interzonal fibres are developed between
centromeres of daughter
chromosomes.Daughter chromosomes
move towards opposite poles.
4. Telophase:
It takes about one hour. It involves
the changes which are opposite to
prophase:
 At each pole, chromosomes are surrounded
by a new membrane formed from ER
elements.
 Chromosomes decondense by hydration and
despiralling to form a network,nuclear
chromatin.
 Astral and spindle fibres are absorbed in
cytoplasm.
 Microtubules undergo depolymerisation of
tubulin subunits.

8.  Centrioles, at each pole, are surrounded by
centrospheres to complete the centrosome.
B.CYTOKINESIS
It involves division of cytoplasm:In animal
cells- cytokinesis starts at metaphase during
which the cell organelles like mitochondria
arrange themselvesequally on either side of
equator During anaphase, the cell membrane
develops a constriction which deepens
centripetally and called cell furrow.In
telophase, cell furrow deepens and finally
divides the cell into two daughter cells.
IN PLANT CELLS, cytokinesis occurs by cell
plate formation.
Significance of mitosis
 It keeps the chromosome number
constant and genetic stability in
daughter cells,so the linear heredity of
an organism is maintained.

9.  It helps in growth and
development of zygote into adult
through embryo formation.
 It provides new cells for repair and
regeneration of lost parts and healing of
wounds.
 Mitosis are similar in all living
organisms showing interrealtionships
between them.
 Mitosis in apical meristems of
plant helps in longitudinal growth.
Thankyou
Presentation by:
Sukhmani ( L-2018-BS-315-M )
Lovepreet( L-2018-BS-306-M)
MSc zoology (sem-1)