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biology
module 2
cell division
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Mitosis
Type of cell division used for growth and
repair
and
asexual
production
How does mitosis and meiosis differ?
- Meiosis has
two
rounds of genetic separation and cellular division while mitosis only has
one
of each.
- In meiosis homologous chromosomes separate leading to
daughter
cells that are not genetically
identical.
- in meiosis the cell are genetically
different
from parent cells, they contain
half
the number of chromosomes
Name the stages of
mitosis
-
interphase
-
prophase
-
metaphase
-
anaphase
-
telophase
-
cytokinesis
The three group phases in interphase
G1
phase = cell grow,
bigger
and replicated organelles
S
phase =
cell replicates DNA
G2 phase = cell keeps growing until all
organelles
have
duplicated
once the DNA has replicated, each ________________ now consist of two sister ______________ connected by structure called _____________
chromosome
chromatids
centromere
Function of mitochondria and ribosome in cell division
Mitochondria produces
ATP
for
energy
Ribosomes, synthesises high level of
proteins
to
replicate
organelles
Prophase
- chromosomes
condense
- Nuclear envelope
disintegrates
- Centrioles move to
opposite
poles of the cell, and form
spindle fibres.
Metaphase
-
chromosomes
line along the middle of the cell.
- Attached to
spindle fibres
by their
centromeres
Anaphase
-
centromere
split
- chromatids pull to
opposite
poles of cell
Telophase and Cytokinesis
- chromosomes
decondense
(become long and thin)
-
Nuclear
envelope reforms around the two new
nuclei.
-
Cytoplasm
divides
- Plasma membrane pinches off
- Two
genetically
,
identical
cells of formed
Gametes
Haploid
cells such as an
egg
or sperm
- unite during
sexual reproduction
to produce a
diploid zygote
Haploid
An organism or cell having only
one
complete set of
chromosomes.
diploid zygote
fertilized
egg
- contain
46
chromosomes (
23
pairs)
Meiosis
Cell division that produces
reproductive
cells in
sexually reproducing
organisms
- involves
meiosis
I and
meiosis
II
Meiosis I:
Interphase
DNA replication
> two identical copies of each chromosome (
chromatids
)
Meiosis I:
prophase
I
chromatids
condense
ad arrange themselves into
homologous
pairs (bivalents)
>
crossing over
occurs
>
nuclear
envelope disintegrates and
spindle fibre
form
Meiosis I:
Metaphase
I
homologous chromosomes line up along the equator and attach to the
spindle fibre
by their
centromeres
Meiosis I:
Anaphase
I
homologous
chromosomes are
separated
Meiosis:
Telophase
1 and
cytokinesis
Chromosomes
reach opposite poles of the cell
>
nuclear envelope
reforms around the chromosomes
>
cytokinesis
results in formation of
two daughter cells
Meiosis II:
Prophase
II
> chromosomes
condense
> nuclear envelope
disintegrates
> spindle fibres
form
Meiosis II:
Metaphase
II
chromosomes attach to the
spindle fibre
by their
centromeres
Meiosis II:
Anaphase II
sister chromatids
are separated
Meiosis II:
Telophase
II
chromatids reach opposite poles of the cell
>
nuclear envelope
reforms and
cytokinesis
takes place
>
4
genetically
unique
daughter cells
2 ways meiosis increases genetic variation
-
crossing over
-
independent assortment
crossing over
- during
prophase
I
- when
homologous
chromosomes move towards each other and exchange
genetic
material
-
chromatid
from maternal chromosome twist around paternal chromosome and connect through
chiasmata
- piece of chromosomes are
exchanges
and the chromatids
separate
- forms chromosomes with different
combinations
of alleles
chiasmata
X-shaped regions where
crossing
over occurred.
independent assortment
- depends on order in which chromosomes line up along the equator of the cell during
metaphase
- different combinations of
chromosomes
will end up in each
gamete
- way
chromosomes
align themselves on the
spindle fibre
is completely random
- results in huge number of possibilities of
chromosomal
combinations in the
gametes
stem cells
unspecialised cells
that have the ability to become specialised
cells
( eg. heart cells or neurones)
cell differentiation
process by which a
stem cell
is
converted
from an unspecialised cell to a specialised cell
how can stem cell be produced
have
unlimited capacity
to divide by
mitosis
potency
stem cells undergoing
differentiation
4 levels of potency
-
totipotent
-
pluripotent
-
multipotent
-
unipotent
totipotent
ability to
divide
into any type of cell
- including
extra
embryonic cells which make up placenta and
umbilical
cord
pluripotent
can divide into any type of cell except
extra embryonic
cells
Multipotent
cells can be divided into a handful of
different
cell types
Unipotent
cell can only divide into
one
type of cell
example of multipotent adult stem cells
adult bone marrow
> divided and differentiated to
replace
old
blood cells
where are stem cell present in plants
in the
meristem
> found in the tip of the
shoots
and
roots
> they can
divide
into any kind of cell
Uses of stem cells in medicine
-
stem cell transplants
- developing ways of growing whole
organs
stem cell transplant
given to patients with
leukaemia
> type of cancer that
destroys
stem cells so
bone marrow
transplant used to replace the lost stem cells
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