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Charlie C

on 11 October 2014

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Transcript of Meiosis

Where Do I Happen?
My Stages!
How Do I Occur?
When Do I Happen?
Meiosis occurs in the tissues called testes (testis) - male genitalia - in men, while in women it occurs within the tissues called ovaries.

More specifically, it occurs in the nucleus of this specialized cell. These are the places where sperm and eggs are formed, respectively.

For females, meiosis is called oogenesis. It produces oocytes, bearing mature eggs. Male meiosis is called spermatogenesis, producing sperm. They do not happen at the same time.

Meiosis occurs in a series of stages:
Why Do I Occur?
What Am I?
In Summary...
By: Esi Aboagye, Paulina Busa, Abigail Colmenar

Meiosis is a type of cell division (sexual reproduction) in which four daughter cells contain half the number of chromosomes as opposed to the parent cell, leading to the production of gametes (a mature male or female germ cell) in animals and spores in plants.
Meiosis occurs to produce haploid cells (which contain half the number of chromosomes) from diploid cells (containing 46 chromosomes), which function as gametes in sexual reproduction. This process leads to increased genetic variation through recombination, which allows a species to have possible future variations in the environment.

The cell divides twice resulting in four cells. They will each have half the number of chromosomes but will carry information from both parents.
Interphase 1
During this stage chromosomes replicate in order to prepare for meiosis. The cell's chromosomes double, consisting of two identical strands of DNA.
Prophase 1
The DNA coils tightly and individual chromosomes are visible under the microscope.
Every chromosome consists of identical sister chromatids joined at their centromeres.
Snynapsis occurs (when a pair of homologous chromosomes line up closely together).
Spindle fibres start to form and nuclear envelope disintegrates.
Crossing over occurs (when a pair of homologues chromosomes exchange DNA between adjacent chromatids).
After crossing over sister chromatids are no longer identical.
Metaphase 1
During Metaphase 1 homologues chromosomes line up along the equator of the cell.
The chromosomes end up on either side of the equator at random.
This results in gametes with different combinations of parental chromosomes. The process is called independent assortment.
Once the chromosomes are lined up, the spindle fibers attach to each centromere.

Anaphase 1
During anaphase 1 the chromosomes move away from one another along the spindle fibers to opposite side of the cells.
Each chromosome is still double stranded and has two sister chromatids.
Telophase 1
During Telophase 1 the spindle fibers disintegrate.
Cellular reproduction and general growth and repair of the body.
The genetic information is identical to the parent cell.
Chromosome Number
Splitting of Centromeres
The centromeres split during Anaphase.
Type of Reproduction
Asexual reproduction.
Occurs In
Mitosis occurs in all organisms.
Number of Divisions
One division.
Number of Daughter Cells
Two diploid cells are produced.
The chromosome number remains the same in both the parent and daughter cells.
Cytokinesis 1
This is where the one cells finally separates and become two separate cells. However, the two cells which form are haploids because they only have half of the chromosomes of their parent cells.
The stages of Mitosis are:
Everything is created except for reproductive cells.
Discovered By
Walther Flemming
Meiosis 2
(Second Division)
This division is the same as mitosis and the cells produced have the same number of chromosomes as the original cell at the end of Meiosis 1.
Prophase 2
During prophase 2 there are two cells which each have two chromosomes.
The spindle fibers form at the poles of the cell.
Metaphase 2
During Metaphase 2 the chromosomes line up along the equator.
Each cell only has one of each homologous chromosome, whereas in Metaphase 1 they were in pairs.
During anaphase 2 the sister chromatids move away from each other along the spindle fibers.
Telophase 2 and Cytokinesis
Through these two stages four genetically different haploid cells are formed.
Mitosis vs. Me
The genetic information in the parent cell differs from the genetic information in the daughter cells.
Chromosome Number
The number of chromosomes in each daughter cell is divided by two, compared to the parent cell.
Genetic diversity through sexual reproduction.
The centromeres do not split during Anaphase 1, but during Anaphase 2.
Splitting of Centromeres
Number of Divisions
Two divisions take place in Meiosis.
Number of Daughter Cells Produced
Four haploid cells are produced.
Type of Reproduction
Sexual reproduction.
Occurs In
Humans, animals, plants, fungi.
Meiosis 1:
Prophase 1, Metaphase 1,
Anaphase 1, Telophase 1

Meiosis 2:
Prophase 2, Metaphase 2,
Anaphase 2, Telophase 2
Meiosis creates reproductive cells only: female egg cells or male sperm cells.
Discovered By
Oscar Hertwig
Meiosis occurs right before birth in females and constantly after puberty in males. Females possess nearly their full amount of partially developed eggs at birth, males produce sperm after puberty from tens of millions to billions a day. When meiosis produces sperm all four of the resulting cells are used. When eggs are produced only one survives. The other three disintegrate after creation.
Meiosis is a type of cell division resulting in four different daughter cells, each with half (23) the number of chromosomes in the parent cell (46). This is the way in which evolution occurs.
Difference between Meiosis and Mitosis
Full transcript