Meiosis+!

=MEIOSIS=

Meiosis is a form of sexual reproduction in which consists of Meiosis I and Meiosis II. In Meiosis I, the mother (diploid) creates 2 cells, each of them haploid. In Meisos II, both haploid cells formed previously in Meiosis I divide in a mitosis-like way to make 4 individual haploid cells (daughter).

__Cells Involved__

//Somatic cells// - These cells have the exact DNA in the organism it is in. Also, these consist of all of the cells except the germ cell. //Germ cells -// These cells consist of about half of the DNA in a somatic cell, which is why it is not part of one. Also, these are the cells that are for secual reproduction. //Gamete cells -// These cells, during sexual reproduction, get together (one from each sex) to form a zygote. //Diploid cells -// These consist of homologous chromosomes, which means that they consist of two pairs or sets of chromosomes. //Haploid cells -// These cells consist of only one set of chromosomes rather than two like a diploid cell. //Polyploid cells -// These cells consist of three or more homologous chromosomes (two). //Anaeuploid cells -// These cells have a nuber of homologous pairs of chromosomes that are unsual and abnormal.

__The Stages__


 * __Meiosis I__**

//Prophase I -// By using synapsis, the homologous chromosomes pair up to form a shape called a tetrad. A tetrad is the form of a 'X'. Crossing over occurs in this stage, which is when sister chromatids exchange genetic information with each other randomly. After this occurs in the cell, the daughter haploid cells are not identical to the mother anymore, for they now have a bit of their mother and father.



//Metaphase I -// In this stage of meiosis, the tetrads formed in the previous stage line up at the equator of the cell, which is the middle of the cell. They are preparing to be pulled apart.



//Anaphase I -// In this stage, the tetrads, which are already lined up, separate. So, the homologous pairs of chromosomes are split and each goes to the opposite side of the cell as they are being pulled apart with their two chromatids by the spindle fibers.

//Telophase I / Cytokinesis -// In this stage, the cell splits in two, each with their own homologous set of chromosomes which were pulled apart in anaphase I. A cell plate forms in between and there are now two separate haploid cells.

//Interkinesis -// The break period between both divisions for the cell to rest for a while.


 * Meiosis II (Mitotic division in each daughter cell)**

//Prophase II -// A spindle (new) reforms itself.

//Metaphase II -// In this stage, the individual chromosomes in each cell line up at the cell's equator, preparing to be split.



//Anaphase II -// The sister chromatids, already lined up at the equator of the cell, are pulled apart and separated from each other. They are pulled by the spindle fibers to opposite poles of the cell.

//Telophase II -// In each cell, two nuclei are formed and each have a haploid amount of chromosomes (one set).

//Cytokinesis -// Each cell splits and the end result of meiosis is four daughter cells (haploid).

__Just The Facts:__

Meiosis consists of two divisions: Meiosis I and II, both which are broken down into steps above. The purpose of meiosis is not because it is short and simple, especially since mitosis is half the steps and requires less energy. It's main purpose is to create genetic diversity. It does this through crossing over. In crossing over, new genes and variation are created. That way, no two cells are the same, since the daughter cells have different combinations of their father and their mother. The chances of being an exact duplicate are rough, especially since the sperm (male gamete) has to enter the egg (female gamete) in order for the implantation and sexual reproduction to take place. Crossing over must happen precisely and in the same portion in each chromosome in order for the genetic exchange to be successful.

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