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Meiosis, condensed.

What Is Meiosis?

Meiosis is the formation of gametes; the sex cells used in sexual reprod­uction (egg and sperm cells).
Usually, during interp­hase, body cells are diploid cells; they contain a full set of chromo­somes (2n). Gametes are haploid (n). Each parent's gametes contain half the genetic material needed, so when a gamete from each parent fuse together, the offspring has a full set of genetic material (2n); half from each parent.

The Stages of Meiosis

1) Interphase
DNA within the cell is duplic­ated.
2n 4n
2) Prophase I
Chromo­somes form homologous pairs (tetrads), and crossing over occurs, where certain genes from each chromosome physically interact and swap over.
3) Metaphase I
Tetrads line up at the equator of the cell.
4) Anaphase I
Spindle fibers pull 1 chromosome from each tetrad to opposite poles of the cell.
5) Telophase I
A cleavage furrow forms, which pinches the cell in the middle.
6) Cytoki­nesis
The cell divides into 2 daughter cells.
4n 2n
7) Prophase II
The reformed nuclear envelope breaks down.
8) Metaphase II
Chromo­somes line up at the cell's equator.
9) Anaphase II
Each chromo­some's sister chromatids are pulled to opposite poles of the cell by spindle fibers.
10) Telophase II
A cleavage furrow forms.
11) Cytoki­nesis
Each daughter cell divides into 2 cells, forming a total of 4 haploid cells for the whole process.
2n n

What Causes Genetic Variation?

Indepe­ndent assort­ment, which occurs when chromo­somes randomly line up at the equator.
Crossing over, during prophase I, where genetic material is swapped by chroma­tids.
Random fertil­isa­tion. During sexual reprod­uction, only one sperm will fertilise one egg, meaning it is random chance which combin­ation of genetic inform­ation will be present in the parents' gametes.

Meiosis Diagram

How Are Mitosis and Meiosis Different?

Number of cell divisions
Number of daughter cells
Genetic compos­ition of daughter cells
Role in animals
Tissue growth, asexual reprod­uction
Formation of gametes (for sexual reprod­uction)


this is so outragous i cryed

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