Mitosis , Meiosis
and the Cell
Cycle
By: Alexus Greene
What is Meiosis?
Meiosis is a cell division process for
reproduction. During this process sex cells or
“gametes” are created. Meiosis is important
because without it you will not be able to
produce the egg or sperm to make a baby.
Phases of Meiosis
Interphase I
The cell increases in mass and prepares for cell division. The cell
synthesizes protein and continues to grow in size.
 Prophase I & II
During Prophase the nuclear envelope and the nuclei disappear,
and the spindle starts to form. As DNA condensates the
chromosomes become visible. The chromosomes with two
chromatids become visible and begin to condense.
 Metaphase I & II
Tetrads line up, and the spindle at this point has been completely
formed. Genetic recombination begins, but only begins once there
are tetrads.
 Anaphase I & II
Tetrads pull apart and chromosomes with two chromatids move
toward the poles. Chromosomes split so that one chromosome with
a chromatid can go toward each pole.
 Telophase I & II
Chromosomes with two chromatids de- condense and a nuclear
envelope reforms around them. Each nucleus is now haploid.

Purpose?
At the end of meiosis I, each chromosome
still had two chromatids. That is double the
amount of DNA that a cell should have. So,
the entire reason to go through meiosis II is
to reduce the amount of DNA back to
normal basically, to split the chromosomes
so that each daughter cell has only one
chromatid per chromosome.
What is Mitosis?
Mitosis is a process of cell division that results
in two daughter cells and its purpose is to
repair and replace die and/or damaged
cells. Mitosis is important because our body
needs new cells in certain parts of our
bodies every second and Mitosis makes
sure that it happens.
Phases of Mitosis
Interphase
The DNA replicates and remains loosely coiled “Messy DNA”. The nuclear
membrane is stable to protect the DNA molecules from undergoing mutation.
 Prophase
DNA molecules shorten then condense to form chromosomes the nucleolus and
nuclear membrane become invisible. The spindle apparatus moves to the
opposite poles.
 Metaphase
Spindle fibers attach to centromeres of the chromosomes and align.
 Anaphase
The spindle fibers shorten and the centromere splits, separated sister chromatids
are pulled along behind the centromeres.
 Telophase
The chromosomes reach the poles. The nuclear envelope reforms before the
chromosomes uncoil. The spindle fibers dissolve.
 Cytokinesis
This is the last stage of mitosis. It is the process of splitting the daughter cells apart.
A furrow forms and the cell is split in two. Each daughter cell contains the same
number and same quality of chromosomes.

Purpose?
Before mitotic division DNA is replicated to
produce; Two identical chromatids
attached by a centromere. This is necessary
so that each new daughter cell formed
receives one copy of each chromosome.
What is the Cell Cycle?
The cell cycle, or cell-division cycle, is the
events that take place in a cell leading to
its division and duplication. These events
include Mitosis, Cytokinesis, and Meiosis.
Cell Cycle Regulation
Cycling
Cycling undergo a constant cycle of synthesis and splitting during cell
division. When cycling are synthesized, they are like activating proteins
and bind to Cdks forming a cyclin-Cdk complex; It is a message to the
cell to pass to the next cell cycle phase. The cyclins degrades,
deactivating the Cdk,.
 G1 cyclins
G1 cyclins attach to Cdk proteins. When the cell reaches the correct
size and the cellular environment is correct for DNA replication, the
cyclins begin to degrade. G1 cyclin degradation deactivates the Cdk
and leads to entry into S phase.
 Mitotic Cyclins
Mitotic cyclins happens during G2. Once they reach a high enough
concentration, they can bind to Cdks. When mitotic cyclins bind to
Cdks in G2, the resulting complex is known as Mitosis-promoting factor
(MPF). Once the mitotic cyclin degrades, MPF is inactivated and the
cell exits mitosis by dividing and re- entering G1.

Cancer from Cell Division??
It is a fact that due to an undivided cell, cancer can
occur. In the article “ Critical pathway in cell cycle
may lead to cancer development” the source is Salk
Institute for Biological Studies; Published July 11, 2013.
From this article I have learned that the cell cycle
causes cancer because when the cells divide they
become shorter than the original cell; when that
happens the cell either becomes inactive or dies.
Activating some enzymes can stop this from
occurring; it is a process called telomerase.
Telomerase prevents the shortening of cells when
being duplicated, this helps it to continue growing
which can lead to uncontrolled cell growth, which
leads to cancer.
Cited Sources
 http://www.diffen.com/difference/Meiosis
_vs_Mitosis
 http://www.biology.arizona.edu/cell_bio/t
utorials/cell_cycle/cells3.html
 Google Images