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Mitosis and Meiosis

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Steven Student

on 13 April 2013

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Transcript of Mitosis and Meiosis

Mitosis and Meiosis Similarities and Differences How are Mitosis and Meiosis similar? http://micro-scopic.tumblr.com/post/29061928178/cancer-cell-division-coloured-scanning-electron
They are both types of cell division. Both processes take one cell and turn it into multiple cells. The number of resulting daughter cells depends on whether mitosis or meiosis is being carried out.

Replication of chromosomes occurs in both mitosis and meiosis. Mitosis leads to the replication of cells and meiosis leads to the replication of organisms.

Both mitosis and meiosis happen inside the nucleus of the cell and go through the same stages known as prophase, metaphase, anaphase and telophase. Cytokinesis completes the division. During mitosis, cells undergo one division which results in two daughter cells that are identical to each other and to the parent cell.

If the parent cell is diploid (2N), then the daughter cells are also diploid. If the parent cell is haploid (1N), then the daughter cells are also haploid. This can occur in some plant species.

The process of mitosis maintains a consistent chromosome number.

Mitosis: 2N → 2N or 1N → 1N How are mitosis and meiosis different? http://www.phoenix5.org/glossary/mitosis.html Mitosis During meiosis, cells undergo two separate divisions which result in a reduction of the chromosome number.

In the first division, the chromosome pairs split and in the second division, the sister chromatids split.

The four daughter cells (gametes) that result are haploid with half the chromosomes of the parent cell. Each daughter cell contains genetic information from both parents.

Meiosis: 2N → 1N Meiosis http://faculty.stcc.edu/BIOL102/Lectures/lesson9/meiosis.htm Mitosis is used for growth of the organism and tissue repair. It also occurs during binary fission when prokaryotes and single celled eukaryotes reproduce asexually.

Meiosis is used to produce gametes for sexual reproduction.

Mitosis occurs in all organisms, including single celled species, in somatic (body) cells.

Meiosis occurs in humans, animals, plants and fungi in germ cells.

Mitosis can produce any cell – skin, bone, blood etc. – except sex cells.

Meiosis can only produce sex cells (sperm and egg cells). More Differences Mitosis consists of Interphase, Prophase, Metaphase, Anaphase, Telophase and Cytokinesis.

Meiosis consists of two divisions. The first is known as Meiosis I and includes: Interphase I, Prophase I, Metaphase I, Anaphase I, Telophase I and Cytokinesis.

The second division is known as Meiosis II and consists of: Interphase II, Prophase II, Metaphase II, Anaphase II, Telophase II and Cytokinesis.
Comparison of the Stages: Mitosis vs Meiosis Interphase http://www.phschool.com/science/biology_place/biocoach/mitosisisg/end.html The same things happen at this stage in both mitosis and meiosis: growth, normal cell function, and DNA replication.

The only difference is that maternal and paternal chromosomes are being replicated in cells undergoing meiosis. Prophase of Mitosis Prophase I of Meiosis http://www.sparknotes.com/biology/cellreproduction/mitosis/section1.rhtml Prophase of Mitosis Similarities in both include:
Chromatin condenses.
Sister chromatids join at centromeres.
The nuclear envelope and nucleolus break down.
The centrioles begin to move to the poles and a spindle forms. Prophase I of Meiosis Prophase I of meiosis is more complex than prophase in mitosis.

Homologous chromosomes (homologs) pair together to form tetrads. This pairing is known as synapsis. The homologs have one maternal and one paternal chromosome and they are held tightly together by a protein lattice.

Each homologous pair is called a tetrad (four) because there are two chromosomes and they each consist of two sister chromatids. So there are a total of four sister chromatids in each tetrad. It is while the chromosomes are in synapse that chiasmata occur. This is the “crossing-over” of neighboring arms of chromosomes.

This crossing-over allows for the exchange of genes between the maternal and paternal chromosomes and results in greater genetic diversity in the gametes which are produced. Crossing-Over http://www.stanford.edu/group/hopes/cgi-bin/wordpress/2011/02/an-introduction-to-dna-and-chromosomes-text-and-audio/ Prophase I of Meiosis Metaphase of Mitosis Metaphase I of Meiosis The centrioles are now at opposite ends of the cell in both mitosis and meiosis.

However, the way the spindle fibers attach is different in metaphase and metaphase I.

In metaphase, the spindle fibers from both centrioles attach to each one of the chromosomes.

The chromosomes line up on the metaphase plate or equator of the cell. http://www.phschool.com/science/biology_place/labbench/lab3/metaphase.html In metaphase I of meiosis, the spindle fibers from each centriole attach to one chromosome of a homologous pair.

The chromosome pairs line up on either side of the metaphase plate.

The way the pairs align is random so that each daughter cell has a 50-50% chance to get either the maternal or paternal homolog for each chromosome.

This random arrangement is known as independent assortment and it increases the genetic diversity of the gametes. www.phschool.com/science/biology_place/biocoach/meiosis/metai.html Metaphase I in Meiosis Metaphase in Mitosis Anaphase of Mitosis Anaphase I of Meiosis The similarity here is that the cell stretches form the force of things being split and pulled towards the poles, but the things splitting are different.

In Anaphase of Mitosis, the centromeres divide in two and spindle fibers pull the sister chromatids apart and they move towards opposite poles.

Each spindle fiber brings one chromatid to its end of the cell. http://www.phschool.com/science/biology_place/labbench/lab3/anaphase.html Anaphase of Mitosis In Anaphase I of Meiosis, the homologs are pulled apart.

Half of the chromosomes move towards one pole and the other half move to the other pole.

The centromeres do not split and each spindle fiber brings two sister chromatids to its end of the cell. http://www.phschool.com/science/biology_place/biocoach/meiosis/anai.html Anaphase I in Meiosis Telophase of Mitosis Telophase I of Meiosis In both mitosis and meiosis, the cell continues to elongate as the daughter nuclei form at the poles.

New nucleoli and nuclear envelopes are formed.

Chromosomes uncoil and reappear as chromatin.

This is the last stage of mitosis as the division of the nucleus is now complete.

Cytokinesis will divide the cytoplasm and complete the division of the cell. http://www.phschool.com/science/biology_place/labbench/lab3/telophas.html Telophase in Mitosis www.digitalwebb.com/Downloads/LabBench/learning/mitosis/cytokin.html
Cytokinesis in Meiosis I separates two haploid cells.

It is important to note that each of these cells now contains half the normal number of chromosomes.

For this reason, meiosis I is referred to as a reduction division.

Each chromosome still consists of two sister chromatids.

The two daughter cells now enter Meiosis II. In telophase I of meiosis, the spindle fibers pull the homologs towards opposite poles to create two haploid chromosomes sets.

If the dividing cell has two equal sized nuclei, then it is a male sperm cell.

In females, most of the cell’s cytoplasm will be concentrated in one of the two emerging cells creating one large cell and one small cell.

The large cell will go on to Meiosis II while the small cell (polar body) will eventually degenerate. http://www.phschool.com/science/biology_place/biocoach/meiosis/teloi.html Telophase I in Meiosis Mitosis is complete and the identical daughter cells enter the GI phase of Interphase. Mitosis and Meiosis I Interphase II Cells may enter a brief period of rest between cell divisions known as Interkinesis or Interphase II.

Other cells may go straight on to meiosis II.

Chromosomes do NOT replicate during this phase. Meiosis II Prophase II of Meiosis http://www.phschool.com/science/biology_place/biocoach/meiosis/proii.html There are two cells dividing in Meiosis II because these are the two daughter cells from Meiosis I.
The chromosomes condense, spindles form, and the centrioles begin to separate. The nuclear envelope fragments. Metaphase II of Meiosis This stage resembles metaphase in mitosis because each chromosome consists of two chromatids.

The centrioles are at opposite poles and fibers from both ends attach to each one of the chromosomes.

The chromosomes line up on the metaphase plate. Spindle fibers begin to pull on each one of the chromosomes from opposite directions. http://www.phschool.com/science/biology_place/biocoach/meiosis/metaii.html Metaphase II of Meiosis Anaphase II of Meiosis http://www.phschool.com/science/biology_place/biocoach/meiosis/compana.html As in anaphase in mitosis, spindle fibers pull the sister chromatids apart and towards opposite poles. Telophase II of Meiosis The chromatids reach the poles and new nuclear envelopes form.

The chromosomes decondense and the spindle disappears.

With meiosis in females, there is only one dividing cell at this point.

As happened in telophase I, the cytoplasm of the cell will be concentrated in one of the two emerging cells.

The resulting large cell will become an egg cell. The smaller cell will eventually degenerate. http://www.phschool.com/science/biology_place/biocoach/meiosis/teloii.html Telophase II in Meiosis http://mitosisandmeiosis.wikispaces.com/cytokinesis The cytoplasm of the cell divides during cytokinesis.

There are now four haploid daughter cells.

Each of these gametes has one set of chromosomes or half the chromosomes of the initial cell. Advantages Advantages of Mitosis

Occurs very quickly.

Large quantities of cells.

Occurs throughout life. Advantages of Meiosis

Genetic diversity.

Ability to adapt to change.

Develop resistance to disease Disadvantages Disadvantages of Mitosis

Lack diversity – all identical.

Vulnerable to change – all wiped out.

Vulnerable to disease – all wiped out.
Disadvantages of Meiosis

Slower – need to find mate.

Fewer offspring.

Need to wait for sexual maturity.  
Bibliography www-mtl.mit.edu/news/archives/2012/08/new_study_finds.html
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