Meiosis

• Prophase 1


  Chromosomes condense, line up with homologous pairs, centrosomes move, spindles form, and nuclear envelope breaks down
• Prophase 1(Crossing Over)


  1. Homolgs associate along their length, with DNA molecules of 2 nonsister chromatids breaking at precise points

  2. Synaptonemal complex (zipper-like protein complex) forms, attaching the homolog pairs

  3. After the complex is formed, they are in synapsis, and DNA breaks are closed when they are joined to corresponding segments of nonsister chromatids, creating cross-overs

  4. After the complex disappears, the homologs are still attached and the locations they are connected are chiasmata
• Prophase 1


  Makes recombined chromosomes because sections of genes on each non-sister chromatid in each homolog pair (tetrad) swap with each other
• Metaphase 1


  Homologous chromosomes line up at the metaphase plate, with chromosomes facing opposite poles. Independent assortment because the homolog pairs line up independently of one another.
• Telophase 1 and Cytokinesis


  Each half of the cell has a complete haploid set of duplicated chromosomes. All the chromosomes have chromatids that have regions of non-sister chromatid DNA
• Metaphase II


  Chromosomes are in the middle of the cell in a single file line. Sister chromatids are NOT identical. Kinetochores of sister chromatids are attached to microtubules extending from opposite poles.