Biology meiosis

• Meiosis


  • Reduces the amount of genetic information
  • Produces haploid gametes
  • Yields four daughter cells with half the number of chromosomes of the parent cell

  
• Gametogenesis


  The process of producing gametes or sex cells
• Oogenesis


  The process of producing egg cells in females

  
• Spermatogenesis


  The process of producing sperm cells in males

  
• Fertilization


  The union of gametes of sex cells to form a diploid zygote
• Interphase


  Has three stages: G1 (first gap), S (synthesis stage), and G2 (second gap)
• 23 pairs of chromosomes

  
• 22 pairs of body cells or autosomes
• 1 pair of sex chromosomes

  
• After Interphase there are 46 chromosomes and 92 chromatids

  
• First meiotic division


  1. Reduces the number of chromosomes (reduction division)

  2. Often accompanied by cytokinesis

  
• Prophase I


  1. Leptonema: Replicated chromosomes have coiled and are already visible

  2. Zygonema: Homologue chromosomes begin to pair and twist around each other (synapsis, bivalent tetrad)

  3. Pachynema: Chromosomes become much shorter and thicker

  4. Diplonema

  5. Diakinesis: Four chromatids of each tetrad are even more condensed, chiasma often terminalize

  
• Metaphase I


  Synapsed tetrads are found aligned at the metaphase plate
• Anaphase I


  Chromosomes in each tetrad separate and migrate toward the opposite poles, sister chromatids (dyads) remain attached at centromere regions

  
• Telophase I


  Dyads complete migration to poles, new nuclear membranes may form, cytokinesis often follows producing two haploid daughter cells

  
• After Meiosis I there are 23 chromosomes and 46 chromatids in each daughter cell

  
• Prophase II


  Dyads contract
• Metaphase II


  Centromeres are directed to the equatorial plate and then divide
• Anaphase II


  Sister chromatids (monads) move away from each other and migrate to opposite poles
• Telophase II


  Monads are at the poles, forming two groups of chromosomes, nuclear membranes form, chromosomes uncoil and extend

  
• After Meiosis II there are 23 chromosomes and 23 chromatids in each of the four daughter cells

  
• Meiosis


  • Reduces the amount of genetic information
  • Produces haploid gametes
  • Yields four daughter cells with half the number of chromosomes of the parent cell
• Gametogenesis


  The process of producing gametes or sex cells
• Oogenesis


  The process of producing egg cells in females

  
• Spermatogenesis


  The process of producing sperm cells in males

  
• Fertilization


  The union of gametes of sex cells to form a diploid zygote
• Interphase


  Has three stages: G1 (first gap), S (synthesis stage), and G2 (second gap)
• • 23 pairs of chromosomes
  • 22 pairs of body cells or autosomes
  • 1 pair of sex chromosomes

  
• After Interphase: 46 chromosomes, 92 chromatids

  
• First meiotic division


  1. Reduces the number of chromosomes (reduction division)

  2. In most cases, the division is accompanied by cytokinesis

  
• Prophase I


  1. Leptonema: Replicated chromosomes have coiled and are already visible

  2. Zygonema: Homologue chromosomes begin to pair and twist around each other in a highly specific manner

  3. Pachynema: Chromosomes become much shorter and thicker

  4. Diplonema

  5. Diakinesis: The four chromatids of each tetrad are even more condensed and the chiasma often terminalize or move down the chromatids to the ends

  
• Metaphase I


  The synapsed tetrads are found aligned at the metaphase plate (the equatorial plane of the cell) instead of only replicated chromosomes

  
• Anaphase I


  Chromosomes in each tetrad separate and migrate toward the opposite poles. The sister chromatids (dyads) remain attached at their respective centromere regions
• Telophase I


  The dyads complete their migration to the poles. New nuclear membranes may form. In most species, cytokinesis follows, producing two daughter cells. Each has a nucleus containing only one set of chromosomes (haploid level) in a replicated form

  
• After Meiosis I: 23 chromosomes, 46 chromatids
• Prophase II


  Dyads contract
• Metaphase II


  The centromeres are directed to the equatorial plate and then divide
• Anaphase II


  The sister chromatids (monads) move away from each other and migrate to the opposite poles of the spindle fiber
• Telophase II


  The monads are at the poles, forming two groups of chromosomes. A nuclear membrane forms around each set of chromosomes and cytokinesis follows. The chromosomes uncoil and extend

  
• After Meiosis II: 23 chromosomes, 23 chromatids