Meiosis …. Part II - PowerPoint PPT Presentation

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Meiosis …. Part II

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  1. Meiosis …. Part II

  2. Metaphase I: ☺ The bivalents have moved to the center ofthe cell ☺ The nuclear envelope has disappeared ☺ The spindle has been fully formed andbivalents have ceased movement toward theequatorial plate ☺ The homologues of each bivalent are coorientedin a position midway between thepoles and are still joined at the previouslyformed chiasmata

  3. Metaphase I

  4. Anaphase I: ☺ The chromosomes move from the metaphaseplate to the poles ☺ The centromeres of a homologue in abivalent remain functionally undivided asthey move poleward so that wholechromosome instead of chromatidssegregate ☺ Each anaphase group is made up of acomplete haploid set of chromosomesinstead of a diploid number of chromatids asin mitosis ☺ Each anaphase group has a 2C DNA content

  5. Anaphase I

  6. Telophase I: ☺ The movement of chromosomes to therespective poles is completed ☺ The spindles disappear ☺ The chromosomes go into diffuse interphasestage ☺ A nuclear membrane and nucleoli is formed(i.e. dyads in monocots) ☺ Division of cytoplasm (i.e. cytokinesis) mayoccur or may be delayed until mitosis II iscompleted

  7. Telophase I

  8. Overview of Meiosis I

  9. Prophase II: ☺ The chromatids condense into easilyrecognized structures from their relaxuncoiled state in the preceding interstage nucleus ☺ No S period of DNA synthesis occursbetween the two mitotic divisions

  10. Metaphase II: ☺ The spindles appear and attach to thechromosomes ☺ Sister chromatid pairs are aligned near the spindle with centromeres still associated ☺ The centromeres orient toward oppositepools and are lined up on the metaphase plate(this is called auto-orientation to distinguishthe process from co-orientation of bivalentsat metaphase I)

  11. Metaphase II

  12. Anaphase II: ☺ The kinetochores separate longitudinally ☺ Sister chromatid pairs separate with onemember of each pair moving toward thepoles

  13. Telophase II & Cytokinesis: ☺ Chromatids reach opposite poles andpoleward movement ceases ☺ New nuclear envelope is formed around eachdiploid chromosome set ☺ Chromosomes begin to de-condense ☺ Cytokinesis follows, and the fate of theresulting four haploid cells depends onwhether the organism is an animal or plant,and male or female

  14. Telophase II & Cytokinesis

  15. Overview of Meiosis II

  16. Thank you