Explains the cell division in Prokaryotes which involve mitosis and meiosis.

1. MITOSIS
KHADIJA SAEED

2. CELL DIVISION
• 2 kinds of cell division:
• Mitosis: division of somatic cells.
• Meiosis: creation of new sex cells.

3. CELL CYCLE
• A typical cell goes through a process of growth, development and
reproduction called the cell cycle.
• Most of the cycle is called interphase.

4. CELL CYCLE
• The longest phase in the
cell cycle is interphase.
• The 3 stages of
interphase are called
G1, s and G2

5. WHAT IS MITOSIS?
• A type of cell division that results in two daughter cells each having
the same number and kind of chromosomes as the present
nucleus.

6. CHARACTERISTICS OF MITOSIS
• A diploid cell wall gives rise to a diploid cell.
• Chromosomes number remains the same.
• The DNA remains identically the same.
• One cell (2n) gives rise to two cells (2N).

7. STAGES OF MITOSIS
• Mitosis is referred to in the
following stages
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

8. PROPHASE
1) Largest phase of mitosis
2) Chromatin condenses into
chromosomes
3) The nuclear envelope
breaks down
4) The centrioles near the
nucleus begin to separate
and move to opposite
sides of the cell.
5) A spindle starts to form
6) Spindles are fibers that are
made out of microtubules.

9. METAPHASE
1) Spindle fibers attach to
the centromeres of each
pair of the sister
chromatids.
2) The sister chromatids
line up at the equator, or
middle of the cell.
3) The spindle fibers ensure
that the separation of
the sister chromatids
goes well.

10. ANAPHASE
• Chromosomes break at
centromeres and the
sister chromatids move
to opposite sides of the
cell.

11. TELOPHASE
1) During telophase, the cell prepares to
repeat it’s cycle.
2) The chromosomes begin to uncoil
and break down
3) A new nuclear membrane forms

12. CYTOKINESIS
• THE CYTOPLASM SPLITS IN
TWO AND THE CELL DIVIDES.

13. CYTOKINESIS
1) The division of the
cytoplasm
2) In animal cells, a
cleavage furrow forms
and separates daughter
cells.
3) In plant cells, a cell plate
forms and separates
daughter cells.

14. REASONS FOR MITOSIS
• There are three main reasons:
• Growth
• Repair/healing
• Asexual reproduction

15. CELL DIVISION BY MITOSIS
• Some cells divide
constantly:
• Cells in the embryo
• Skin cells
• Gut lining cells etc.

16. MEIOSIS
KHADIJA SAEED

17. MEIOSIS
DEFINITION:
• A type of cell division that results in
 four daughter cells
 each with half the number of chromosomes of the parent cell,
 production of gametes
• Diploid (2n) Haploid (n)
• TWO DIVISIONS:
i. Meiosis I
ii. Meiosis II

18. MEIOSIS I
PHASES:
• Prophase I
• Metaphase I
• Anaphase I
• Telophase I

19. INTERPHASE I
• Similar to mitosis interphase
• sister chromosomes replicate (s phase)
• Each duplicated chromosome consist
of two identical sister chromatids
attached at their centromeres.
• Centrioles pairs also replicate.

20. PROPHASE I
o Longest and most complex phase
(90%)
o Chromosomes condense
o Synapsis occurs:
o homologous chromosomes come
together to form a tetrad.
o Also called crossing over.
o Tetrad is two chromosomes or four
chromatids.

21. Stages of prophase 1

22. METAPHASE I
• Shortest phase
• Tetrads align on the
metaphase plate.
• Independent assortment
occurs:
• Orientation of homologous
pair to poles is random.

23. ANAPHASE I
• Homologous chromosomes separate and move towards the poles.
• Sister chromatids remain attached at their centromeres..

24. TELOPHASE I
• Each pole now has haploid set of chromosomes.
• Cytokinesis occurs and two haploid daughter cells are formed.

25. OVERVIEW
crossing over

26. MEIOSIS II
• Prophase II
• Metaphase II
• Anaphase II
• Telophase II

27. PROPHASE II
• Chromosomes coil and become
compact(if uncoiled after
telophase 1)
• Nuclear envelope and nucleolus,
if reformed, disappears again.
• Centriole move to opposite
poles, forming spindle fibers
between them

28. METAPHASE II
• Individual duplicated chromosomes align on the equator.
• One chromosome per spindle fiber attached by means of kinetochore of
centromere.
• Centriole has reached the poles.

29. ANAPHASE II
• Spindle fibers contract.
• Duplicated chromosomes split
in half (centromere dividing in
two.
• Sister chromatids separate and
move to opposite poles.

30. TELOPHASE II
• Daughter chromosomes has reached the poles.
• Two cells invaginate and form 4 daughter haploid cells (gametes)
• They uncoil and form chromatin.
• Nuclear envelope and nucleolus form around chromatin again.
• Centrioles form centromere.

31. OVERVIEW

32. RESULT OF MEIOSIS
• Gametes (egg and sperm
form)
• Four haploid cells (n) with
one copy of each
chromosome
• One allele of each gene
• Different combinations of
alleles for different genes
along the chromosome.

33. EASY WAY TO REMEMBER THE STAGES:
 P : Preparation
 M : Middle
 A : Away
 T : Two
PMAT