Meiosis

• Meiosis is a form of cell division that gives rise to genetic variation. The main role of meiosis is production of haploid gametes as cells produced by meiosis have half the number of chromosomes. Meiosis produces genetically different cells
• Meiosis: Crossing over of chromatids where pairs of chromosomes line up and exchange some of their genetic material and independent assortment of chromosomes – there are various combinations of chromosome arrangement
• This form of cell division is a two phase process in which four haploid gametes are generated from a diploid cell. During meiosis I, homologous chromosomes separate therefore there is only one chromosome of every pair per gamete, whereas in meiosis II the sister chromatids separate.
• The stages of meiosis I are prophase I, metaphase I, anaphase I and telophase I.
• Prophase I closely resembles the prophase stage of mitosis, with the exception of synapsis and crossing over of homologous chromosomes (at chiasmata) which allow the genetic exchange to occur.
• Metaphase I is when each pair of bivalents align at the equator. The position of each bivalent is random (Random assortment) and this contributes to genetic variation.
• During anaphase I, the homologous chromosomes separate whereas during telophase I the nuclear envelope reforms around haploid nuclei containing half the number of chromosomes.
• During meiosis II composed of prophase II, metaphase II, anaphase II and telophase II, another round of cell division occurs, leading to formation of four haploid daughter cells, containing single chromosomes. It is during Anaphase II that the centromeres split separating chromatids.