1. Meiosis Guided Notes Ramshaw – Biology

2. Interphase… • Interphase happens at the start of _____________ as well as mitosis. • Prior to prophase I, the cell goes through the G1, S, and G2 phases of ________________.

3. Prophase I(chapter 10) • DNA coils into ___________ chromosomes, spindle fibers appear, nucleus disappears. • Every chromosome is paired up next to its ______________ (the chromosome that is the same size and shape). • This is called _____________ and does not occur in mitosis.

4. Prophase I (cont.) • Each pair of homologous chromosomes is called a ______________. • When chromosomes line up next to each other, “____________ ______” occurs and they exchange pieces of DNA. • This is called _________ recombination. Crossing over Only one cross over is shown but many occur per pair.

5. So why is Crossing Over SO important????? • Reasons why:

6. Review of Key Terms • Homologue (Homologous Chromosomes): • Synapsis • Tetrad • Crossing Over

7. Metaphase I • _____________ line up in the center of the cell next to each other. • Spindle fibers from one centriole attach to the centromere of one _________ chromosome then spindle fibers from the opposite centriole attach to the other homologous _____________.

8. Anaphase I • Each homologous chromosome moves to the _____________ pole. • This __________ separation of homologous chromosomes is called ________________ assortment. • It separates the chromosomes you inherited from your mom and dad and creates new combinations of ________ on each chromosome!

9. Telophase I • Chromosomes reach the opposite ends of the ______, new nuclei form in each new cell, and spindle fibers __________. • The new cells are ___________!

10. To review… What are the major events in Meiosis I?… • Prophase I: • Metaphase I: • Anaphase I: • Telophase I:

11. NO INTERPHASE HERE • There is no interphase between _____________ 1 and ____________ 2. This is very important because there is no S phase!!! (no doubling of the ________!!!)

12. Start of Meiosis II Prophase II • Centrioles form and move toward the __________ • The nuclear membrane ________________

13. Metaphase II • __________ fibers attach from the centrioles to the centromeres • The __________ chromatids line up along the cell equator

14. Anaphase II • The centromeres __________ and sister chromatids separate  • The cell starts to ______ apart

15. Telophase II – Cytokinesis • The cell pulls _____________ apart – forming new nuclei, one in each cell • Cytokinesis reaches completion, creating ___ haploid ____________ cells

16. These 4 haploid cells then create: • ______________! • If the organism going through meiosis is a female, only ___ of the cells becomes the egg, the others become “_______ Bodies” and are dissolved by the body. This process of making an egg is called __________________. • If the organism going through meiosis is a male, _____ __ cells become spermatids which mature in to sperm. This is called _______________________.

17. Major events in Meiosis! • The cell starts out by doubling the _____ in Interphase: After S1 phase (Sister chromatids) Copy of Chromosome (doubling the DNA) A chromosome before the S1 phase Original Chromosome

18. After Interphase is… • Prophase I • _____________ and crossing over occur • Lets draw that out!

19. Then comes: • Metaphase I – Homologous chromosomes line up in the _________ of the cell next to each other. • Anaphase I – The __________ are pulled apart, one to each side of the cell • Telophase I – Two ___________ cells are formed

20. Then the second part - Meiosis II • Prophase II – Nucleus _______________ • Metaphase II – Chromosomes line up _________ file down the middle of the cell • Anaphase II – Sister chromatids are pulled ___________ towards opposite ends of the cell • Telophase II – 4 __________ cells are formed