MODULE 11 MEIOSIS

• Meiosis produces 4 daughter cells, each with half number of chromosomes, compared to single parent cell

  •Process gives rise to HAPLOID CELL from DIPLOID CELL
• Meiosis 1 Reductional division, chromosome number reduce by half (46 to 23)
• Prophase 1 divided into 5 substages

  •Leptonema

  •zygonema

  •Pachynema

  •Diplonema

  •Diakinesis
• Leptonema( thin threads)

  •Chromosome show condensation and feplication
• Zygonema pairing and twisting of homologous chromosomes

  •SYNAPSIS occur
• Tetrad/Bivalent pair consist of four chromatids
• Pachynema shorter and thicker chromosomes

  •crossing over occur which is genetic material exchanging
• Diplonema bivalent chromosomes unbutton themselves resulting in separation of two homologous chromosomes or (two pairs of sister chromatids separated from each other)

  •Inner chromatids or two non sister chromatids remain attached referred as CHIASMA
• Diakinesis homologous chromosome completely separate from each other and regain their infividual identity

  •Nuclear envelop disappear and spindle fibers enter
• Metaphase 1 homologous chromosomes arranged on equator (plane equidistant) form metaphase plate.

  •Spindle fibers from one pole of cell attached to one chromosome of each pair (sister chromatids) and other attach to homologous chromosome
• Anaphase 1 homologous chromosome separate from each other and moves towards opposite pole
• Anaphase 1 sister chromatids remain attached to each other as they go to opposite poles
• Telophase 1

  Homologous chromosomes complete their migration

  •nuclear membrane and nucleolous begin to reappear

  •haploid set of chromosomes is at each pole, with each having two chromatids
• Meiosis 2 equational cell division similar to mitosis
• Propase 2 chromosomes start re condense or condense and become short and compact

  •nuclear membrane and nucleolus start vanishing

  •formation of spindle fibers
• Metaphase 2 single chromosomes align at the equator forming the metaphase plate

  •Kinetochores of the sister chromatids face the opposite poles, and each attached to kinetochore microtubulr coming from the pole
• Kinetochore protein structure that forms on a chromatid during cell division and allows it to attach to a spindle fiber on the chromosome
• Anaphase 2 two sister chromatids separate from each other and move to opposite pole due to contraction of spindle fibers
• Telophase 2 chromosomes decondense
• Cytokinesis is the divison of cytoplasm in cells and helps separate each cell into two haploid cells
• After meiosis 1 there are

  23 chromosomes

  46 chromatids
• After meiosis 2 there are

  23 chromatids and chromosomes