complete cell division. mitosis and meiosis.

1. By- Dr. Saurabh Anand
Thawrani
Guided by- Dr. R.S.

2. Contents
• Introduction
• Types of cells
• Types of cell divison
• Cell cycle
• Mitosis
• Meiosis
Meiosis I
Meiosis II
• Applied aspects

3. Introduction
What is it?
The process by which a parent cell divides into two or
more daughter cells. Cell division usually occurs as part
of a larger cell cycle. In eukaryotes, there are two
distinct types of cell division: a vegetative division,
whereby each daughter cell is genetically identical to the
parent cell (mitosis), and a reproductive cell division,

4. • Cell division is an inherent property of living
organisms. It is a process in which cells
reproduce their own kind.
• The growth, differentiation, reproduction and
repair take place through cell division.
• Rudolf Virchow(1858) suggested ”Omnis
cellula e cellula” means every cell is derived
from pre existing cell.
• There are two types of cell division namely
Mitosis and Meiosis.

5. • The cell (from Latin cella, meaning "small
room")
• The basic structural, functional, and biological
unit of all known living organisms.
• A cell is the smallest unit of life that
can replicate independently, and cells are often
called the "building blocks of life".
• Prokaryote is a single-celled organism that
lacks a membrane-
bound nucleus (karyon), mitochondria, or any
other membrane-bound organelle.

6. Types of cell division

7. Cell cycle
•The cell cycle is the sequence of events or changes that occur
between the formation of cell and its division into daughter cells.
•It has a nondividing, growing phase called Interphase and
dividing phase called mitotic or M-phase.

9. Interphase ( inter – between, phases – aspect)
:metabolically active phase
• Longest phase in the cell cycle
• Cell grows in size
• Doubles cytoplasmic organelles
• Duplicates chromosomes
• Three stages: G1, S, G2
1. G1: cell growth
2. S: synthesis of DNA (chromosome duplication)
3. G2: cell growth and preparation for division

10. G1 Phase or GAP 1 Phase :
• Period in the cell cycle during interphase, after
cytokinesis and before the S phase.
• The cell is metaboically active,
• There is great amount of protein and enzymes
synthesis,
• There is NO DNA REPLICATION
S-Phase or Synthesis Phase :
• Period in the cell cycle during interphase,
between G1 phase and the G2 phase.
• DNA synthesis or replication occurs.

11.  G2 Phase or GAP 2 Phase:
• The final, and usually the shortest phase during
interphase
• Cell undergoes a period of rapid growth to prepare for M
phase.
• The nucleus is well defined, bound by a nuclear
envelope and contains at least one nucleolus.
• At the end of this phase is a control checkpoint (G2
checkpoint) to determine if the cell can proceed to enter
M phase and divide.
• G2 checkpoint prevents cells from entering mitosis with
DNA damaged since the last division, providing an
opportunity for DNA repair and stopping the proliferation
of damaged cells so that the G2 checkpoint helps to
maintain genomic stability
 G 0 Phase (Quiescent stage) :
• Period in the cell cycle where cells do not divide further
and exist in a quiescent state.

12. Mitotic or M-phase
• The most dramatic period of the cell cycle,
involving a major reorganisation of virtually all
components of the cell.
• Since the number of chromosomes in the
parent and progeny cells is the same, it is also
called as equational division.
• It includes two important processes that occur
simultaneously.
Karyokinesis (division of the nucleus)
Cytokinesis (division of the cytoplasm)
• Resulting in two daughter cells.

13. Mitosis
(Gr. Mitos – thread, osis – stage)
• Walter Flemming (1882) studied mitotic cell
division in animal cells and coined the term
mitosis.
• Mitosis is a type of cell division in which a parental
cell produces two similar daughter cells that
resemble the parental cell in terms of
chromosomal number. Hence called Equational
cell division (homotypic cell division).
• This maintains constant number of chromosomes
in each cell of successive generation.
• It occurs in somatic cells of the body. Also called

14. Karyokinesis (Karyon – nucleus, kinesis –
movement)
The division of nuclear material.
• Occurs in four stages
1. Prophase (Gr. Pro – before, phases –
appearance)
2. Metaphase (Meta – after, phase –
appearance)
3. Anaphase (ana – up, phases - appearance)
4. Telophase (Telo – end, phases –
appearance)

15. Prophase (Gr. Pro – before, phases –
appearance)
• It is the longest phase.
• The chromatin is organized into distinct
chromosomes by coiling or spiralization.
• The centrioles develop into asters and move
towards the opposite poles of the cell to
establish the plane of cell division.
• Spindle apparatus begin to appear
• Nucleolus and Nuclear membrane disintegrate
and disappear
• The chromosomes are set free in the

16.  Centromere : It is the primary constriction in chromosome to which
the spindle fibres attach during mitotic and meiotic division. It appears
as a constriction when chromosomes contract during cell division.
After chromosomal duplication, which occurs at the beginning of
every mitotic and meiotic division, the two resultant chromatids are
joined at the centromere.
 Spindle fibres : It is a group of microtubules that extend from the
centromere of chromosomes to the poles of the spindle or from pole
to pole in a dividing cell.
 Sister chromatids : During S phase of the cell cycle the DNA is
replicated and an identical copy of the chromatid is made. These
identical copy of chromatids are called sister chromatids.

18. Metaphase (Meta – after, phase –
appearance)
• Spindle fibres are completely formed
• The chromosome become short and thick with
two distinct chromatids each
• All the chromosomes move towards the centre
of the cell and arrange in the equatorial plane,
right angles to the position of asters to form
metaphasic plate
• Chromosomes are attached to spindle fibres at
their centromeres

19. Metaphase plate :
The plane of the equator (a plane that is equally
distant from the two spindle poles) of the
spindle into which chromosomes are positioned
during metaphase

21. Anaphase (ana – up, phases - appearance)
• The centromere of all the chromosomes undergo
longitudinal splitting and the chromatids of each
chromosome separate to form daughter chromosomes
• The daughter chromosomes move toward the
opposite poles from the equator by the activity of
spindle fibres

23. Telophase (Telo – end, phases –
appearance)
• During this, the events of prophase will be
reversed
• The daughter chromosomes reach the opposite
poles
• The chromosomes undergo despiralization to form
long, thin thread like structures called chromatin
• Nucleolus and nuclear membrane reappears
• The spindle fibres disappear

25. Cytokinesis (cyto – cell, kinesis –
movement)
The Division of cytoplasm
• A cleavage furrow develops in the middle of the
cell in centripetal direction due to the
contraction of microtubules.
• It occurs till the edges of the plasma membrane
meet.
• They fuse to form a separate membrane.

26. Overview

27. Significance of Mitosis:
• It maintains genetic stability within
the population of cells derived
from same parental cell
• It helps the growth and tissue
repair
• It helps in the replacement of dead
and worn out cells
• It is a means of reproduction in

28. SUMMARY
• Type of cell division which takes places during
growth, repair and replacement.
• Takes place in somatic cells.
• Basis of asexual reproduction.
• Daughter cells identical in chromosome
number and genetic make-up at the parent
cell.
• Ensures consistency of genetic information in
nuclei of cells of one individual.
• Chromosomes don’t arrange themselves
along equator in homologous pairs during
metaphase.

30. • Derived from the Greek word meaning
'lessening'.
• The term meiosis (originally spelled "maiosis")
was introduced to biology by J.B. Farmer
and J.E.S. Moore in 1905
• This is a special method of cell division,
occurring in maturation of the sex cells, by
means of which each daughter nucleus
receives half the number of chromosomes
characteristic of the somatic cells of the
species.

31. • Meiosis I is initiated after the parental
chromosomes have replicated to produce
identical sister chromatids at the S phase.
• Meiosis involves pairing of homologous
chromosomes and recombination between
them.
• Four haploid cells are formed at the end of
meiosis II.
• Homologous Chromosomes :
Homologous chromosomes are
chromosomes in a biological cell that pair
(synapse) during meiosis and contain the

32. Sequence Of Events
Meiosis I
(reductional division)
Karyokinesis I
Prophase I
a) Leptotene
b)Zygotene
c)Pachytene
d)Diplotene
e)Diakinesis
Metaphase I
Anaphase I
Telophase I
Cytokinesis I
Meiosis II
(mitotic meiosis)
Karyokinesis
II
Prophase II
Metaphase II
Anaphase II
Telophase II
Cytokinesis II

33. MEIOSIS I
It is reductional division in which a
diploid parental cell produces two
haploid daughter cells. Hence it is
called reductional division

34. Prophase I; longest phase (5
stages)
a) Leptotene: (bouquet stage)
• The chromatin condenses to form chromosomes
• The chromosomes appear as long, thin and thread
like structures. They undergo coiling and become
short and thick.
• Each chromosome has two chromatids that are not
distinctly visible.
• Each chromosome shows bead like structures
called chromomeres.
• The telomeric ends of all the chromosomes
converge towards one side of nuclear membrane;

35. b) Zygotene (Zipper stage):
• Pairing of homologous chromosomes takes place
called synapsis. The pair is called bivalent.
• The chromosome continues to undergo
condensation and asters keep moving towards
opposite poles.
c) Pachytene (Tetrad stage):
• The chromosomes become more short and thick
• Each bivalent shows four chromatids called tetrad
• In this stage the exchange of genetic material
takes place between the non sister chromatids of
homologous chromosomes.
• This process is called genetic crossing over.
• This results in genetic recombination which is

36. d) Diplotene:
• The chiasma move towards the tips of
chromosomes as the homologous
chromosomes of bivalent start moving apart.
This event is called Terminalisation
e) Diakinesis:
• The chromosomes at this stage appear thick,
short and distinct
• The tips of some chromosome show chiasma
• Nucleolus and Nuclear membrane disappear

38. Synapsis: Pairing of the homologous
chromosomes is called Synapsis
Bivalent: A paired unit formed of homologous
chromosomes consisting of a paternal and a
maternal chromosome is called Bivalent
Tetrad: Each homologous chromosome pair
(bivalent) shows four chromatids called tetrad
Crossing over: Exchange of identical parts
between the nonsister chromatids of
homologous chromosomes is called Crossing
over.
Chiasma: These are the regions on homologous

39. Metaphase-I
• Chromosomes are arranged in the equatorial
region with their centromeres towards the poles
and arms towards the equator.

40. Anaphase-I
• The Centromeres do not under go longitudinal
splitting
• The chromosome of each homologous pair
move towards opposite poles by the activity of
spindle fibres. This is called separation or
disjunction of chromosomes.

41. Telophase-I
• The homologous chromosomes separate and reach the
opposite poles
• The nuclear membrane reappears around the
chromosomes at each pole
• The spindle fibres disappear
• Cytokinesis occurs

42. Cytokinesis 1-
It is the division of cytoplasm.
Interkinesis-
The Interphase after the first meiotic division
is called Interkinesis.
It may be present or absent between meiosis-I
and meiosis-II.
If present it may be short or in some cases
telophase-I directly enters to prophase-II.
It is similar to Interphase except for the
absence of replication of DNA.

43. Meiosis II
Occurs soon after meiosis-I.
There is no duplication of
chromosomes.
Hence called mitotic meiosis

44. Prophase-II
• The chromosomes start condensing again
• Spindle apparatus begin to appear
• The nuclear envelope and nucleolus
disintegrate and disappear

45. Metaphase-II
• The Chromosomes arrange in the equatorial
region at right angles to the asters
• The Spindle fibres connect to the centromere.

46. Anaphase-II
• The centromeres of all the chromosomes undergo
longitudinal splitting.
• The chromatids of each chromosome separate and
they move towards opposite poles.

47. Telophase-II
• The chromosomes arrive at the poles and undergo
decondensation to become thin and long chromatin fibres.
• A nuclear envelope is formed.
• Nucleolus also appears
• The spindle fibres disappear

48. Overview (Meiosis I)

49. Overview (Meiosis II)

50. Significance of Meiosis
• It helps to restore diploidy and maintain
the constant number of chromosomes for
a species.
• Meiosis produces new combination of
chromosomes and genes by crossing over
and by a random distribution of paternal
and maternal chromosomes to daughter
cells.

51. SUMMARY
• Location - gonads.
• Reduction division - results in halving number
chromosomes.
• Cell division involved in gamete production.
• Four daughter cells formed. Male - all four
develop. Female - three abort, one develops.
• Two divisions occur.
• Chiasma formation leading to crossing over occurs
prophase I resulting in a mixing of genetic material
of the chromosomes.
• Metaphase I - bivalents arrange themselves on
equator of cell. Results in further variation as
random which may position themselves.
• Anaphase I - chromosomes separate.

53. Applied aspects
Defective Mitotic Division
• It usually results in the production of
uncontrolled growth of cells or defective cells.
• Uncontrolled Mitosis
• If the genes that regulate the cell cycle are
damaged or mutated, cell divides abnormally or
may lead to uncontrolled cell growth.
• Cause may be due to Harmful ray: nuclear
radiation, UV ray, Viruses, Carcinogenic
chemicals: food additives, benzo (α) pyrene in

54. Micronuclei
• Micronuclei are extranuclear cytoplasmic bodies.
• They are induced in cells by numerous genotoxic agents that
damage the chromosomes.
• The damaged chromosomes, in the form of acentric
chromatids or chromosome fragments, lag behind in
anaphase when centric elements move towards the spindle
poles.
• After telophase, the undamaged chromosomes, as well as the
centric fragments, give rise to regular daughter nuclei. The
lagging elements are included in the daughter cells, too, but a
considerable proportion is transformed into one or several
secondary nuclei, which are, as a rule, much smaller than the
principal nucleus and are therefore called micronuclei.
• Bigger micronuclei result from exclusion of whole
chromosome following damage to the spindle apparatus of
the cell, whereas smaller micronuclei result from structural
aberrations; causing chromosomal fragments.

56. Defective Meiotic Division
• Defective meiotic divisions usually result in the
production gametes with chromosomal
numerical abnormalities
• Down Syndrome - trisomy of chromosome 21
• Patau Syndrome - trisomy of chromosome 13
• Edward Syndrome - trisomy of chromosome
18
• Klinefelter Syndrome - extra X chromosomes
in males - i.e. XXY, XXXY, XXXXY, etc.
• Turner Syndrome - lacking of one X
chromosome in females - i.e. X0

57. References
• http://www.biologyreference.com/Gr-Hi/History-of-
Biology-Cell-Theory-and-Cell-
Structure.html#ixzz4FChB53a6
• Journal of Oral and Maxillo Facial Pathology Vol.
12 Issue 1 Jan - Jun 2008. Clinico-pathological
correlation of micronuclei in oral squamous cell
carcinoma by exfoliative cytology .Devendra H
Palve, Jagdish V Tupkari.
• Vander’s human physiology 8th edition
• Kahel-frotcher- atlas of human anatomy 10TH
edition.
• Color Atlas of Cytology, Histology, and Microscopic
Anatomy4th edition, revised and Enlarged

58. Thank You
