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Istilah mitosis : proses yg menghasilkan dua sel
anak yg identik.
Mitosis memegang peranan dalam pertumbuhan
dan perkembangan organisme.
Pada tanaman mitosis terjadi pd sel-sel
meristematis, misalnya ujung-ujung akar, dan
ujung batang.
Mitosis
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In prophase, the cell begins the
process of division.
1. The chromosomes condense. The
proteins attached to the DNA cause
the chromosomes to go from long thin
structures to short fat one, which
makes them easier to pull apart.
2. The nuclear envelope disappears.
The double membrane that surround
the nucleus dissolves into a collection
of small vesicles, freeing the
chromosomes to use the whole cell for
division
3. The centrosomes move to opposite
poles. During interphase, the pair of
centrosomes were together just
outside the nucleus. In prophase they
separate and move to opposite ends of
the cell.
4. The spindle starts to form, growing
out of the centrosomes towards the
chromosomes.
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Metaphase is a short
resting period where
the chromosomes are
lined up on the equator
of the cell, with the
centrosomes at opposite
ends and the spindle
fibers attached to the
centromeres.
Everything is aligned
for the rest of the
division process to
occur.
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In anaphase, the
centromeres divide. At
this point, each
individual chromosome
goes from:
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1 chromosome with 2
chromatids
to:
2 chromosomes with one
chromatid each.
Then the spindle fibers
contract, and the
chromosomes are
pulled to opposite
poles, towards the
centrosomes.
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In telophase the cell
actually divides.
The chromosomes are at
the poles of the spindle.
The spindle disintegrates
The nuclear envelope reforms around the two sets
of chromosomes.
The cytoplasm is divided
into 2 separate cells, the
process of cytokinesis.
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The organelles (other than the
chromosomes) get divided up into
the 2 daughter cells passively: they
go with whichever cell they find
themselves in.
Plant and animal cells divide the
cytoplasm in different ways.
In plant cells, a new cell wall made
of cellulose forms between the 2
new nuclei, about where the
chromosomes lined up in
metaphase. Cell membranes form
along the surfaces of this wall.
When the new wall joins with the
existing side wall, the 2 cells have
become separate.
In animal cells, a ring of actin fibers
(microfilaments are composed of
actin) forms around the cell equator
and contacts, pinching the cell in
half.
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Produces gametes (sperm and egg cells)
Reduces the number of chromosomes in new
cells to half the number in the original cell
Res
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Perpasangan kromosom yg homolog (synapsis)
Pertukaran bagian kromosom (crossing over)
Distribusi kembali kromosom
Susunan materi genetik mungkin berbeda dg
tetua akibat crossing over
Meiosis I
Meiosis II
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Prophase I
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Prophase II
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Metaphase I
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Metaphase II
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Anaphase I
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Anaphase II
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Telophase I
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Telophase II
Each homologue in the
cell pairs with its partner,
then the partners
separate
Prophase I
Metaphase I
Anaphase I
Telophase I
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Each duplicated, condensed chromosome
pairs with its homologue (synapsis)
Homologues swap segments (crossing over)
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After crossing over, each chromosome contains
both maternal and parental segments
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Creates new allele combinations in offspring
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Chromosomes are pushed and pulled into the
middle of cell
Sister chromatids of one homologue orient
toward one pole, and those of other homologue
toward opposite pole
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Homologous chromosomes segregate from
each other randomly (independent
assortment)
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Independent assortment results in genetic
variation
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The chromosomes arrive at opposite poles
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The cytoplasm divides
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There are now two haploid cells
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This completes Meiosis I
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The two sister chromatids of each duplicated
chromosome are separated from each other
two chromosomes
(unduplicated)
one chromosome
(duplicated)
Prophase II
Metaphase II
Anaphase II
Telophase II
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Microtubules attach to the kinetochores of the
duplicated chromosomes
Chromosomes move toward the spindle’s
equator
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All of the duplicated chromosomes are lined
up at the spindle equator, midway between
the poles
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Sister chromatids separate to become
independent chromosomes and move to
opposite poles
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The chromosomes arrive at opposite ends of
the cell
A nuclear envelope forms around each set of
chromosomes
The cytoplasm divides
There are now four haploid cells
Meiosis Animation I
Meiosis Animation II
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Mitosis
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Two diploid cells produced
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Each identical to parent
Meiosis
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Four haploid cells produced
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Differ from parent and one another
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
L.
M.
N.
O.
P.
Q.
R.
Tassel
Microsporocyte
Megasporocyte (2n)
Meiosis
Microspore (n)
Germinated pollen grain
Sperm nuclei (n)
Fertilization
Ear shoot
Mature spotophyte (2n)
Endosperm (3n)
Embryo (2n)
Mature kernel (2n)
4 megaspores (n)
Degenerating megaspores
Surviving megaspores
Mature embryo sac
Polar nuclei (n)
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Mikrosporogenesis (pada anther)
Megasporogenesis (pada bunga
betina/ovarium)
Canna
Hibiscus