COMPLETE INFORMATION ABOUT CELL DIVISION UPTO HIGHER LEVEL

1. TOPIC-MITOSIS AND MEIOSIS - THEIR
SIGNIFICANCE AND DIFFERENCES BETWEEN THEM
SOURAV RANJAN NANDA
M.SC
GENETIC AND PLANT BREEDING

2.  Cells, the basic units of all living things, are enclosed by
membranes. Chromosomes, the cellular structures that carry
the genes, are composed of DNA, RNA, and protein.
 In eukaryotes, chromosomes are contained within a membrane-
bounded nucleus; in prokaryotes they are not. Eukaryotic cells
possess complex systems of internal membranes as well as
membranous organelles such as mitochondria, chloroplasts, and
the endoplasmic reticulum.
 Haploid eukaryotic cells possess one copy of each chromosome;
diploid cells possess two copies. Prokaryotic cells divide by
fission; eukaryotic cells divide by mitosis and cytokinesis.
 Eukaryotic chromosomes duplicate when a cell’s DNA is
synthesized; this event, which precedes mitosis, is characteristic
of the S phase of the cell cycle

3. Chromosome-
Chromosomes are thread-like structures
located inside the nucleus of animal and
plant cells
A chromatid is one of the two halves of
a replicated chromosome
The two chromatids that make up a
chromosome are called "sister
chromatids
They are joined at the centromere and
are genetically identical because, during
interphase, one sister of each chromatid
pair is produced by directly copying the
other, pre-existing sister.

4. two sister chromatids of each
chromosome are segregated into
separate cells in both mitosis and
meiosis, but they remain together
throughout meiosis I. It is only
during the second meiotic
division (meiosis II) that they
finally are separated and
distributed into separate cells.

6.  The term mitosis was coined by Fleming (1882)
 Parent cell undergoes mitosis to produce two identical daughter cells which are
similar to parent cell w.r.t. number of chromosomes and kinds of chromosome.
Therefore, mitosis is "so known as equational cell division or homotypic cell
DIVISION
•Based on duration
. Prophase is the longest phase.
Anaphase is the shortest phase

7. Stages of Mitosis
 Interphase
 Prophase
 Metaphase
 Anaphase
 Telophase
 Cytokinesis.

9. Interphase
Phase between two mitotic events.
Chromosomes are fully extended and uncoiled,
It is longest phase , the interphase will take 22-23 hrs.
Gl Phase
RNA and protein synthesis take place .
It takes around 25-50% Of interphase.
Each chromosome consists of single chromatin in Gl phase.
S Phase
DNA synthesis takes place result in production of two sister
chromatids in each chromosomes.
Takes around 35-40% of interphase time.
Histone synthesis also taken place.
G Phase
1. Takes 10-12% of interphase time.

10. Prophase
•Chromosomes undergo condensation
and two chromatids of each
chromosome become visible.
•Plectonemic relational coiling
between sister chromatids is another
•At the end of prophase, nucleolus
disappear, spindle apparatus start
appearing
].

11. Metaphase
1Auto-orientation of chromosomes:
Centromere of all chromosomes lie
on equatorial plate and their arms lie
on either side of the equatorial plate.
This kind of arrangement of
chromosome in mitotic metaphase is
known auto-orientation of
chromosome.
2-Nuclear Membrane disappear

12. Anaphase
1.Centromere , of each homologous
chromosome divides Longitudinal as a
result the two sister chromatids of
each chromosome will separate from
each other and start move towards
opposite pole.
Centromere is the first portion of the
chromosome to move towards pole
and two arms of each chromosome
dangling behind fhe centromere

13. • Decondensation of chromosomes,
nucleolus will reappear and nuclear
membrane is reorganized.
Cytokinesis occurs at the end of
telophase.

14. CYTOKINESIS

15. MEIOSIS
 The reduction in chromosome number is mainly due to
single S phase followed by two successive nuclear
divisions
 Term meiosis was coined by Former and Moore.
 First Meiotic division Known as reduction division : Two
daughter cells produced during first meiotic division will
have half of the chromosome number present in the parent
cell

16. PROPHASE I

18. (a) Leptotene
I. Chromosomes begin to undergo condensation.
2. Chromosomes start appears as fine thread like
structure.
3. RNA and protein synthesis occur.
(b) Zygotene
I. Homologous chromosomes undergo pairing.
2. Remaining 0.3% of DNA undergo replication.
3. Synaptonemal complex is formed.
4. 0.3% DNA replicated during zygotene is
considered to play important role in homologous
chromosomes pairing.

19. synaptonemal complex
Synapsis is usually accompanied by the formation of a
protein structure between the pairing chromosomes .
This structure, called the synaptonemal complex,
consists of three parallel rods—
 the lateral elements -one associated with each of the
chromosomes
 central element -one located midway between them
 A large number of ladderlike rungs connecting the
lateral elements with the central element.
 The role of the synaptonemal complex in
chromosome pairing and in subsequent meiotic
events is not fully understood. In some types of
meiotic cells it does not even appear

20. Pachytene
Condensation of chromosomes continues.
Bivalents are distinctly visible.
Each bivalent has four chromatids known as four strand stage.
Crossing over occurs between two nonsister chromatids of homologous chromosomes.
Diplotene
Homologous chromosomes begin to move away from each other.
Chiasma is visible;
Chiasma terminalization occurs.
Condensation of chromosomes further continues.
Diakinesis
Homologous chromosomes are attached at the telomeric regign and get separated at the end of diakinesis.
Nucleus and nuclear envelop started disappearing.
 Spindle fibre will start organizing. First

22. METAPHASE I
I. Co-orientation of homologous
chromosome
2. Orientation of different homologous
chromosomes on equatorial plate is
random and independent from each
other. It is the cytological basis for
law of independent assortment.

23. ANAPHASE I

24. ANAPHASE I
1. Homologous chromosome will
start moving away from each other
as a result, one chromosome from
each bivalent moves to one pole
and other chromosome will move
to opposite pole.
2. Each chromosome will have two
chromatids (sister chromatids are
intact) after anaphase-I. Each halve
will have half of the chromosomes
of the parent cell.

25. TELOPHASE I
• Partial
uncoiling of
chromosomes
(but not
complete
uncoiling)
• Cell divide into
divide into
dyad during
cytokinesis

26. INTERPHASE
 There is no DNA synthesis in this prophase
 It is absent in many species

27. MEIOSIS II
 PROPHASE II- the chromosomes condense and become attached to a
new spindle apparatus (prophase II).
 METAPHASE II -They then move to positions in the equatorial plane of
the cell
 ANAPHASE II -their centromeres split to allow the constituent sister
chromatids to move to opposite poles (anaphase II), a phenomenon called
chromatid disjunction.
 TELOPHASE II-the separated chromatids—now called chromosomes—
gather at the poles and daughter nuclei form around them. Each daughter
nucleus contains a haploid set of chromosomes.

28. PROPHASE II

29. METAPHASE II

30. ANAPHASE II