Meiosis

• Prophase I

  DNA condenses, chromosomes arrange in homologous pairs (bivalents), which are close togther so swapping over of information at the chiasma can occur, nuclear envelope breaks down, nucleolus disintegrates
• Metaphase I

  Bivalents line at equator, spindle fibre attaches to centromeres, Independent assortment occurs where the chromosomes position themselves independently (% of maternal/paternal is random)
• Anaphase I

  bivalents separated as microtubules pull whole chromosomes to opposite ends of spindle

  Centromeres do not divide
• Telophase I

  Spindle fibre breaks down, nuclear envelopes reform around the 2 groups of chromosomes, nucleoli reform
• Cytokinesis

  Division of cytoplasm,

  Animals : cleavage furrow formed by cell surface membrane pinching inwards

  Plants: Vesicles merge to form new cell surface membrane , secretion of calcium petate becomes middle lamella + cellulose layered

  Ends in 2 haploid cells
• Prophase II

  NB: interphase is skipped - no DNA replication

  Nuclear envelope breaks down, chromosomes condense

  spindle forms perpendicular to old one
• Metaphase II

  Chromosomes line up single file along equator of spindle
• Anaphase II

  centromeres divide, individual chromatids pulled to opposite poles, creating 4 groups of chromosomes
• Telophase II

  Nuclear membranes form around each group of chromosomes
• Cytokinesis

  Cytoplasm divides, creating 4 non-identical haploid cells