STAGES OF MEIOSIS (FINAL)

• Like mitosis, meiosis also refers to how cells divide to produce new cells. Sex cells or gametes are produced from meiotic division.
• Meiosis is the M phase that leads to the production of either sperm cells or egg cells. This type of division is very closely tied with the process of sexual reproduction.
• Meiotic Division: production of functional sex cells or gametes; reduction in the chromosome number; two rounds: meiosis I and meiosis II; allows restoration of original chromosome number during fertilization.
• Meiosis involves two rounds of cytokinesis which will ultimately produce four daughter cells with a reduced chromosome number.
• Meiosis I comes after the G2 phase of the cell cycle. Chromosomes are in sister chromatid conformation. Starts with duplicated chromosomes.
• Meiosis I is a reductional division.
• Prophase I: Condensation, synapsis between homologous pairs, and crossing over.
• Prometaphase I: Chromosomal condensation, disintegration of nuclear envelope, and meiotic spindle formation.
• Metaphase I: Maternal and paternal chromosomes are randomly arranged, alignment at metaphase plate, facilitates reduction in chromosome number.
• Anaphase I: Separation of homologous pairs.
• Telophase I: Formation of daughter cells.
• Prophase II: Preceded by an interkinesis, chromosomes recondense.
• Prometaphase II: Disintegration of the nuclear envelope.
• Metaphase II: Alignment of the duplicated chromosomes.
• Anaphase II: Separation of sister chromatids.
• Telophase II: Formation of daughter cells.
• Synapsis occurs only in meiosis I.
• Crossing over occurs only in meiosis I.
• Tetrads line up and separate into individual homologous chromosomes in meiosis I.
• Sister chromatids line up and separate into individual chromosomes in meiosis II.
• Importance of Crossing Over: facilitates genetic recombination; enhances genetic variation; increases chances of survival.
• Synapsis involves the pairing of the members of homologous chromosomes so as to allow them to undergo crossing over and to segregate them.
• Crossing over refers to the exchange of segments between non-sister chromatids of homologous chromosomes. Ultimately, this enhances the genetic diversity of species.
• Meiosis II is an equational division.