This document summarizes the key stages of mitosis and meiosis. It describes that mitosis occurs in somatic cells and results in two identical daughter cells with the same number and type of chromosomes as the parent cell. Meiosis occurs in germ cells and results in four haploid daughter cells each with half the number of chromosomes as the original diploid parent cell. The document outlines the main phases of the cell cycle, including interphase and the phases of mitosis (prophase, metaphase, anaphase, telophase). It also provides details about the key events and phases of meiosis I and meiosis II, including homologous chromosome pairing, crossing over, and the formation of haploid daughter cells.

1. CELL CYCLE
MITOSIS AND MEIOSIS
DR. DILIP V. HANDE
ASSOCIATE PROFESSOR, DEPT OF BOTANY
SHRI SHIVAJI SCIENCE COLLEGE, AMRAVATI MS.

2. INTRODUCTION:
 The number of cells increases by the
division as preexisting cells.
 The dividing nucleate cells include two
integral activities i.e. The division of
nucleus (karyokinesis) and division of the
cytoplasm (cytokinesis).
 Usually the karyokinesis is followed by the
cytokinesis.
 Some times cytokinesis does not follow
karyokinesis these division results in the
formation of multinucleate cells.

3. CELL DIVISION
 The cell may divide by any one of the
following methods.
Amitosis or direct cell division
Mitosis or indirect cell division
Meiosis or reduction division

4. AMITOSIS
 It is a simple mode of cell division,
generally occurs in unicellular organisms
like bacteria and protozoon.
 It this case the nucleus elongate first
become double shaped forming middle
constriction finally form two nuclei and
later on by constriction the cytoplasm the
two daughter cells get formed .
 In the process there is complete absence
of nuclear events.

5. AMITOSIS

6. MITOSIS
 Mitosis generally occurs in somatic (vegetative) cell.
 It is the process by which cell divides with sets of
chromosome exactly similar to the parent cell.
 Thus number of cells increase without any change in
the genetic composition i.e. structure & number or
chromosome replace and repair of cells in the theory.
 The most convenient material for the study of mitosis
is the root tips of onion.
 The mitotic cycle or cell cycle includes two distinct
phases.
 Inter phase or non dividing period.
 Mitotic phase or cell- division period.

7. INTERPHASE :
 It is called resting period, but during
this period the cell is metabolically
very active.
 In this phase the DNA content is
doubled and also some proteins and
enzymes are synthesized.
 Cell prepare itself for the division.
 It is longest phase of cell division
include 3 sub- phases.

8. CELL CYCLE

9. CELL CYCLE
 G1 phase (gap period):- It is growth phase
during this synthesis of proteins and RNA
takes place and the cell grows in volume.
 S phase :- (synthetic period):- During this
period DNA synthesis occurs i.e replication of
chromosomal DNA takes place which result
in doubling of the chromosomal threads.
 G2 (Gap2):- In this part the volume of cell
increases and it is pre division stage, amount
of DNA and cell content becomes more
synthesis of proteins and RNA takes place.
In this phase chromatin fibers are seen.

10. MITOTIC PHASE:
 Actual cell division occurs in this phase, it
include karyokinesis and cytokinesis.
 Karyokinesis is the division of nucleus into
two daughter nuclei.
 It consist of following phases

11. PROPHASE
 It is the first phase of
mitosis in which cell
becomes spheroid, and
viscous.
 The chromatin material
becomes visible as
separate threads or
chromosomes.
 Each chromatid contains a
single DNA molecule.
 The two chromatids of a
chromosome are connected
by a centromere.
 The nucleolus and nuclear
membrane start
disappearing.
 The chromosomes remain
distributed in nucleoplasm.

12. METAPHASE
 In this phase the
chromosomes reaches the
central or equatorial
portion of the spindle.
 The chromosomes one
lined up in one plane to
form equatorial plate or
metaphasic plate .
 There are two kinds of
spindle fibers.
 Some fibers are long and
extend from pole to pole.
These are called
continuous fibers.
 Other get attached to the
chromosomes at the
centromere these are
called chromosomal fibers.

13. ANAPHASE :
 In this phase the centromers of
each chromosome divides into
two.
 The two sister chromatids of
each chromosome separate
from each other these
chromatids now called as a
daughter chromosomes.
 The two sets of daughter
chromosomes migrate to the
opposite poles of the spindle.
 Probably this movement is
caused due shorting of
chromosomal fibers.
 Depending to upon the
position of centromere the
chromosomes showing shapes
like V,J,L or I (metacentric
submetacentric and
telocentric).

14. TELOPHASE
 This is the last phase in
karyokinesis.
 The two sets of daughter
chromosomes reach the opposite
poles.
 The chromosomes begin to uncoil
and form chromatin networks.
 Nuclear envelope formed around
each set of the chromosomes.
 The nucleoli appear at the site of
nuclear organizer.
 The after telophase two daughter
nuclei are formed due to
karyokinesis.
 Karyokinesis is then followed by
cytokinesis.

15. CYTOKINESIS
 The division of cytoplasm into two
daughter cells is called cytokinesis.
 It is start simultaneously with telophase
stage.
 In plant cells it is accomplished by the
formation of phragmoplast and cell plate.
 The tubular elements of E.R. , vesicles of
Golgi complex reach the equator forming
cell plate.
 This plate grow and join the cell wall. This
plate later convert into the middle lamella.

16. SIGNIFICANCE OF MITOSIS :-
 Mitosis ensures equal distribution of the
nucleus and cytoplasm between the
daughter cells.
 The hereditary material (DNA)is also
equally distributed.
 The constant number of chromosomes in
all cells of the body is because of mitosis.
 Mitosis helps in the growth and
development of the organs and the body
of organisms.
 Mitosis help in the repair of damaged
tissues or organs by producing new cells.
 Mitosis helps in the asexual reproduction
in some organisms.

17. MEIOSIS
 Introduction
 The term meiosis was coined by Former in 1905.
 It occurs only in the reproductive cells which
results in the formation of haploid gametes.
 During meiosis the chromosomes divide once
and the nucleus and cytoplasm divide twice.
 Due to this four haploid cells are formed from
diploid cell.
 Hence it is also called reduction division.
 In this case the haploid daughter cells differ
from each other as well as from mother cell.

18. PROCESS OF MEIOSIS
 The process of meiosis shows a sequences of
events similar to those of mitosis but these events
are repeated twice with or without a short
interphase between them.
 In the first meiotic division the diploid parent cell
divide into two haploid daughter cells, so this
division is also known as Heterotypic division.
 The second meiotic division is a simple mitotic
division.
 This division is also known as the homeotypic
division.
 Each of the two meiotic cell division is further
distinguished into sub stages.
 They are as follows.

19. MEIOSIS-I
 It is the first meiotic division during which
the diploid parent cell gives rise to two
haploid daughter cells.
 It includes the further phases.
 Prophases –I :
 This phase has longer duration. It is
having about 5 phases.

20. LEPTOTENE / LEPTONEMA :
 In this stage the volume
of the nucleus increases.
 Chromosome becomes
uncoiled and long thread
like in shape.
 The chromosomes look
beaded in appearance i.e.
each chromosome has
one centromere and
numerous nucleosomes
(beads).
 The nucleolus and
nuclear envelop is visible.

21. ZYGOTENE / ZYGONEMA :
 In this stage the chromosomes
become shorter and thicker and
pairing of homologous
chromosomes takes place.
 The homologous chromosomes
(one paternal and other maternal)
from the two sets are attracted
towards each other and form pairs.
 In each pair, the two homologous
lie parallel to each other all along
their lengths.
 This pairing is called synapsis and
the paired chromosomes are called
bivalent.
 At this stage each chromosome
appear to have only chromatid.
 Thus each pair has in all two
chromatids.
 Hence each pair is in the dyad
stage.

22. PACHYTENE /
PACHYNEMA
 In this stage the
recombination of characters
(genes) takes place through
a phenomenon called
crossing over.
 The chromosome becomes
shorter, thicker, distinct now
each chromosome has two
sister chromatids joined by
a centromere.
 Thus each pair of the
homologous chromosomes
(bivalent ) at this stage
consist of four chromatids (

23. PACHYTENE / PACHYNEMA
 The non sister chromatids are twisted round
each other and may take part in crossing
over.
 The chromatid is the unit of crossing over.
 Two chromatid belonging to two different
homologues (non- sister chromatids)
undergo one or more breaks at the same
level.
 After the break inter change of chromatid
segments takes place between the non-
sister chromatids.
 The broken chromatid segments unit with
other chromatids due to presence of an
enzyme ligase.
 This process inter change of chromatin

24. D) DIPLOTENE/ DIPLONEMA :
 In this stage the homologous chromosomes
repel each other as the force of attraction
between them decreases.
 The separating chromosomes are held
together at one or more points, where
crossing over occurred.
 These points are called chiasmata. The
number of chiasmata varies with the
length of the chromosomes.
 Generally shorter chromosomes have few
chiasmata than the longer ones.
 By the end of diplotene, the chiasmata
begin to move from the centromere
towards the end.
 This displacement of chiasmata is termed
as terminalization.
 When terminalization is complete the
homologous chromosomes are held
together by the terminal chiasmata.

25. THANKS