1. Chapter 10.3 Visual Tour of Meiosis AP Biology Fall 2010

2. Objectives Describe the events that occur in each meiotic phase

3. Meiosis I Prophase I – Chromosomes become visible as threadlike forms – Each pairs with its homologue and usually swaps segments with it – Microtubules are forming a bipolar spindle – If two pairs of centrioles are present, one pair is moved to the opposite side of the nuclear envelope, which is stating to break up

4. Meiosis I Prophase I

5. Meiosis I Metaphase I – Microtubules from one spindle pole have tethered one of each type of chromosome; microtubules from the other pole have tethered its homologue – Chromosomes aligned midway between the poles

6. Meiosis I Metaphase I

7. Meiosis I Anaphase I – Microtubules attached to each chromosome shorten and move it toward a spindle pole – Other microtubules, which extend from the poles and overlap at the spindle equator, ratchet past each other and push the two poles further apart – Motor proteins drive this process

8. Meiosis I Anaphase I

9. Meiosis I Telophase I – One of each type of chromosome has now arrived at the spindle poles – For most species, cytoplasm divides at some point, forming 2 haploid cells – All chromosomes still duplicated

10. Meiosis I Telophase I

11. Meiosis II Prophase II – A new bipolar spindle forms in each haploid cell – Microtubules have moved one member of the pair of centrioles to the opposite end of each cell – One chromatid of each chromosome becomes tethered to one spindle pole, and its sister chromatid becomes tethered to the opposite pole

12. Meiosis II Prophase II

13. Meiosis II Metaphase II – Microtubules from both spindle poles have assembled and disassemble in a tug-of-war that ended at metaphase II

14. Meiosis II Metaphase II

15. Meiosis II Anaphase II – The attachment between sister chromatids of each chromosome breaks – Each is now a separate chromosome but is still tethered to microtubules, which move it toward a spindle pole – Other microtubules push the poles apart – A parcel of unduplicated chromosomes ends up near each pole – One of each type of chromosome is present in each parcel

16. Meiosis II Anaphase II

17. Meiosis II Telophase II – Four nuclei form as a new nuclear envelope encloses each cluster of chromosomes – After cytoplasmic division, each of the resulting daughter cells has a haploid (n) number of chromosomes

18. Meiosis II Telophase II

19. Meiosis