CELL CYCLE AND CELL DIVISION • CELL CYCLE The orderly sequence of events by which the cell duplicates its contents and divides into two is termed as the cell cycle. The event is genetically controlled. It consists of two periods-(a) interphase (b)mitosis. • MITOSIS Occurs in somatic cells. Equational division. Duplicated chromosomes distributed equally to the daughter cells. Consists of 4 stages –prophase, metaphase, anaphase, and telophase. • MEIOSIS Occurs in germ cells. Involves two sequential cycles that are meiosis I and meiosis II. There is only a single cycle of DNA replication. Meiosis I is initiated after is S phase. Meiosis involves the pairing of homologous chromosomes and recombination between them. Four haploid cells are formed called germ cells.

1. CELL CYCLE AND
CELL DIVISION

2. CELL CYCLE
The orderly sequence of events by
which the cell duplicates its contents
and divides into two is termed as cell
cycle.
The event is genetically controlled.
It consists of two periods-
(a)interphase (b)mitosis.

3. CELL CYCLE
G A P 1 S P H A S E G A P 2
IN TE R P H A S E
K A R Y O K IN E S IS C Y TO K IN E S IS
M O R M ITO S IS P H A S E
C E L L C Y C L E

4. CELL CYCLE

6. MITOSIS
P R O P H A S E M E T A P H A S E A N A P H A S E T E L O P H A S E
K A R Y O K IN E S IS C Y T O K IN E S IS
M IT O T IC D IV IS IO N

7. MITOSIS
Occurs in somatic cells.
Equational division.
Duplicated chromosomes distributed
equally to the daughter cells.
Consists of 4 stages –
prophase,metaphase, anaphase and
telophase.

8. PROPHASE
Chromosomal material condenses into
compact mitotic apparatus.
Each chromosome consists of two
chromatids held together at centromere.
Spindle formation starts.
At the of prophase nuclear
membrane,nucleolus,endoplasmic
reticulum &golgi bodies disappear.

9. METAPHASE
Spindle fibres attach to kinetochores
of chromosome.
Chromosomes are moved to spindle
equator and get aligned along
metaphase plate through spindle
fibres to both poles.

10. ANAPHASE
Centromere split and chromatids
separate.
Chromatids move to opposite
poles.

11. TELOPHASE
Chromosomes cluster at opposite
poles.
Identity of chromosomes is lost as
discrete elements.
Nuclear envelope, nucleolus, golgi
complex & E R reform.

12. CYTOKINESIS
Animal cells-furrows in the plasma
membrane gradually deepens and
ultimately joins in the center dividing the
cell cytoplasm into two.
Plant cells-cell plate formation starts at
the center of the cell and grows outward
to meet existing lateral walls.

13. SIGNIFICANCE OF
MITOSIS
Equal distribution of chromosome
among two daughter cells.
Surface/volume ratio is maintained.
Nucleoplasmic ratio is maintained.
Causes growth of organ.
Replaces worn-out cells.

15. Early prophase
Prophase
Late prophase
Transition to
metaphase
Metaphase
Anaphase
Telophase
DONE
Interphase

16. MEIOSIS
Occurs in germ cells.
Involves two sequential cycles that is meiosis I
and meiosis II.
There is only a single cycle of DNA replication.
Meiosis I is initiated after is S phase.
Meiosis involves pairing of homologous
chromosomes and recombination between
them.
Four haploid cells are formed called germ cells.

17. MEIOSIS
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase II
MEOSIS-I MEOSIS-II

18. MEIOSIS I
L E P T O T E N E Z Y G O T E N E P A C H Y T E N E D IP L O T E N E D IA K E N S IS
M E IO S IS

19. LEPTOTENE
Chromosomes become
gradually visible due to
compaction of
chromosomes.

21. ZYGOTENE
Pairing of homologous chromosomes
take place by the process called
synapsis.
The complex structure formed due
to pairing is called synaptonemal
complex and the chromosomes is
called a bivalent or tetrad.

22. PACHYTENE
Crossing over(exchange of genetic
material) occurs between two non sister
chromatids.
recombination nodules appear at the site
of crossing over.
Enzyme recombinase involves in crossing
over.
Crossing leads to recombination of
genetic material between two
chromosomes.

24. DIPLOTENE
Recombined homologous
chromosomes tends to separate from
each other except at the site of cross
over.
Chromosomes look X shaped called
chiasmata.

26. DIAKINESIS
Terminalisation of chaismata.
Chromosomes are fully condensed.
Meiotic spindle is assembled to
separate homologous chromosomes.
Nucleolus disappear and nuclear
envelope breaks down.

27. METAPHASE I
Bivalent chromosomes arranged at
equatorial plate.
Spindle fibres from opposite poles
attach to to the pair of homologous
chromosomes.

28. ANAPHASE I
Homologous chromosomes
separate, while sister chromatids
remain associated at their
centromere.

29. TELOPHASE I
Nuclear membrane and nucleolus
reappear.
Two cells are formed.
Chromosomes under go dispersion.

30. PROPHASE II OF
MEIOSIS II
Chromosomes become compact.
Nucleolus and nuclear
membrane disappear.

31. METAPHASE II
Chromosomes align at the
equator.
Microtubules from opposite
poles of the spindle get attach to
the kinetochores of sister
chromatids.

33. ANAPHASE II
Centromere of each
chromosome splits and
chromatids(chromosome) move
towards opposite poles of cell.

34. TELOPHASE II
∗ Chromosomes are enclosed by
nuclear envelope.
∗ Nucleolus reappear .

35. SIGNIFICANCE OF
MEIOSIS
Conservation of specific
chromosome number of each
species is achieved.
Increase genetic variability in
organisms which are important
for evolution.