1. Genetic Variation
Meiosis reduces the number of chromosomes and produces haploid cells from diploid cells.

2. Stages of Meiosis - I Interphase Prophase I
DNA is replicated and sister chromatids are joined at the centromere regions
Prophase I
chromosomes condense and pair
crossing-over may occur as DNA segments are exchanged between homologous chromosomes
place of crossing over forms a chiasmata (X-like region that holds the homologues together)
synaptonemal complex holds homologues together and then degrades by the end of the phase
aids in crossing over
formed by a specialized protein complex
the rest is the same as in mitosis

3. Stages of Meiosis - I Metaphase I Anaphase I Telophase I (cytokinesis)
tetrads are now aligned at the metaphase plate
rest like mitosis
Anaphase I
chromosome pairs (sister chromatids) move toward the poles
Telophase I (cytokinesis)
each cell is now haploid but still consists of pairs of sister chromatids
cytokinesis splits the cell and cells are now haploid at 2n = 46

4. Stages of Meiosis - II Prophase II Metaphase II Anaphase II
spindle fibers again grow and sister chromatid pairs move toward the metaphase plate
Metaphase II
chromosomes are now at the metaphase plate but are not genetically identical due to crossing over
Anaphase II
sister chromatid pairs separate at the centromere region and move toward opposite poles
Telophase II (cytokinesis)
nuclei begin to form and DNA begins to uncondense
cytokinesis separates divides the cell
there are now 4 haploid cells (n=23)
each daughter cell is genetically unique

5. Genetic Variation
Genetic variation is made possible through the following processes:
Independent assortment of chromosomes
because the arrangement at the metaphase plate is random, each haploid has a 50% chance that it will receive a parental chromosome
Crossing over
creates recombinant chromosomes that are a mix or both parental chromosomes
Random fertilization
because of random fertilization each individual contains a genetically unique compliment of chromosomes and genes