Transcript The Cell Cycle, Mitosis and Meiosis

The Cell Cycle, Mitosis
and Meiosis
Cell Reproduction
The Cell Cycle
Most of a cell’s time
not spent dividing
G 1: Gap 1 or Growth1: cell is growing after just being created
S stands for Synthesis. DNA is copied before the cell can divide again
G2 is a second growth stage as the cell prepares to divide again
Mitosis is used
to….
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Mitosis is used for
asexual reproduction.
To spread out in a
habitat by making
clones.
It is also used to grow
and develop and repair
injuries
This is a clone of Aspen Trees. They are all genetically identical
There are 4 Steps to Mitosis, and Interphase when cells
are in the G, S and G2 parts of the cell cycle
During the S part of the
Cell cycle, the DNA
Replicates
This creates two identical
pieces of DNA called
sister chromatids
Together the two sisters
Make up a chromosome
Prophase (First phase)
Occurs as the
chromosomes become
visible and the nuclear
membrane begins to
break down.
During Metaphase
(middle phase)
The Chromosomes
Line up in the middle of
The cell. Having been
Pushed and pulled on
By the spindle fibers
Spindle Fibers
Each sister chromatid attaches to
different spindle fibers at the
Kinetochores of the chromatids
During Anaphase (Separate)
The spindle fibers shorten, pulling
the sister chromatids apart to opposite
ends of the cell. Once apart they are now
each called Chromosomes.
Telophase (End phase)
Two nuclei reform, and a new cell wall
called a cell plate is built in plants to
separate the cytoplasm of the two new
daughter cells.
The two daughter cells are identical
to each other and to the parent
cell which created them
Mitosis works fine for
Growth and development
Repair of damaged tissue
But it can’t be used to make egg or sperm cells because…
Egg and sperm cells (gametes) need one half the chromosomes of the
parent cell
Meiosis
Sexual Reproduction in Plants
Meiosis makes cells with 1/2 of the chromosomes as
the parent cell.
In plants this process makes either male microspores
that become sperm, or female megaspores that become
eggs
This process also makes unique cells
In plants a diploid (two sets of
Chromosomes) generation
Does meiosis to make a
haploid (half the number of
Chromosomes) generation.
Homologous Chromosomes
Pairs of chromosomes that control the same traits
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During Meiosis the cell
goes through two
divisions
In the first one, the
homologous cells separate, and
in the second the sister
chromatids separate
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Creating up to 4 cells with half
the number of chromosomes as
the parent cell.
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How does Meiosis create unique
cells?
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During Prophase 1
crossing over happens
to the homologous pairs
to create new
combinations of DNA
Homologous pair
One from mom, one from
dad
Crossing
Over
Unique cells due to crossing over