Note: For more information on any of the terms in this article, see Cell Reproduction.
Meiosis is the process by which a regular diploid body cell divides and becomes 4 haploid gametes. It consists of two stages: Meiosis I and Meiosis II. Meiosis I is the first division of cells and Meiosis II is the second. This process is generally similar to regular Mitosis with a few differences that effect the end products.
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Meiosis I has four phases just like mitosis (Prophase, Metaphase, Anaphase, and Telophase) with some small differences. The results of Meiosis I are two diploid cells with genetic differences on the chromosome. These differences are a result of crossing-over.
Crossing-over is a process that happens after both homologous chromosomes in a pair join up to form a structure called a tetrad. Tetrads form through a process called synapsis. Once a tetrad is formed, a portion of each homologous chromosome breaks off and is re-attached to the same part of its homolouge. This mixes up the traits that are found in each of the chromosomes, thus resulting in genetic recombination.
- Prophase I:
- Metaphase I:
- Anaphase I:
- Telophase I:
Meiosis II is the second round of cell divisions during meiosis and the diploid cells formed during Meiosis I divide again to form two haploid gametes. Between these two stages, interphase is skipped unlike normal mitosis. Because of this, the S phase does not occur and so the DNA in these cells is not copied making the resulting cells form this phase haploid.
- Prophase II:
- Metaphase II:
- Anaphase II:
- Telophase II:
After this process is complete, the end results are four haploid gametes. These cells combine during fertilization to create a diploid cell that has all the DNA needed to replicate normally on its own through mitosis. This also recombines the DNA from the father and mother cells to create an offspring cell with traits from both parent cells.