mitosis

Cell Division

Chapter 5 Form 4

THE CELL CYCLE



MITOSIS



Occurs in somatic cells
which are diploid (2n)

Mitosis

Produces new cells for
growth, repair and replace
dead or damaged cells

Area of cell division Root tip
Root cap
(where mitosis occur)
Meristematic cells

 Process of producing 2 diploid daughter cells with the same
DNA by copying their chromosomes (clones)

 Important of Mitosis
 Growth
 Repair damaged cells
 Replace dead cells
 Asexual reproduction
 Regeneration

 cancers result from uncontrolled mitosis

Process of mitosis

• Prophase
• Metaphase
• Anaphase
• Telophase

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Prophase

• Chromosome
– condensed (shorter)
– tightly coiled

• Nucleolus
– disappears

• Nuclear membrane
– disintegrates (break up)

• Centrioles
– move to opposite poles

• Spindle fibre
– appear

Metaphase Metaphase
plate
Spindle
fibres

• Line up on the metaphase
plate/ equator

Anaphase

• Centromere
– divides/split

• Sister chromatid
– separated/pulled apart
to the opposite poles
(by spindle fibre)

Telophase

• Chromosomes
– reach the pole

• Spindle fibres
– begin to disappear

• Nuclear membrane
– forms around each
set of chromosomes
to form two nuclei

• Nucleolus
– reappears in each nucleus

CYTOKINESIS

In animal cell

• Occurs to divide cytoplasm into two daughter
cells

In plant cell

• Cytokinesis starts with the formation vesicles
• The vesicles grows outward until it fuses with the

plasma membrane and forms cell plate.
• Cell plate divides the cell into two daughter cells
• Cell walls are formed at both sides of the cell plate
• Two daughter cells are formed



TISSUE
CULTURE



CLONING

DEFINITION
Cloning is a process of producing clones which
are genetically identical copies of a cell, tissue,
or an organism through asexual reproduction.

ANIMAL CLONING
Involves the transfer of the nucleus from a
somatic cell to an ovum or embryonic cell with
the nucleus removed.

•Cloning is a form of asexual reproduction because
the organisms produced have the same genetic

content and chromosomal number as the parent
organism.
•The first successfully cloned animal was a sheep,
named Dolly in 1996.



DOLLY, THE FIRST CLONED ANIMAL

1. Somatic cells are removed and grown in a culture
medium. The starved cells stop diving and enter a non-
diving phase.

2. An unfertilised egg cell (ovum) is obtained. The
nucleus is removed, leaving only the cytoplasm and
organelles without any chromosomes.

3. An electric pulse stimulates the fusion between the
somatic cell and the unfertilised ovum.

4. The cell divides repeatedly, forming an embryo.
5. The embryo is implanted into a surrogate mother.
6. Dolly is born.

Transgenic crops Plants take a Allows
which are resistant shorter period to
to herbicides, pests, biotechnologists to
grow multiply copies of
and diseases useful genes or
Advantages
are created of cloning clones

Control Can be produced in

environmental a shorter time and in
pollution large number

Vegetative
reproduction :

- no pollinating
agents is needed,
propagation can take
place at any time

Natural equilibrium No genetic Shorter lifespan
variation
-may be disrupted
as the clones may Disadvantages
undergo natural of Cloning

mutation

All clones have Genes resistant
the same level of to herbicide

resistance
towards certain

diseases