1. To be successful today…
Pick up graded Notebooks
Pull out why meiosis notes
BYOD Color of the day is Phones are in put away in backpacks

2. After warm up: Add to TOC & Glue in pages
NOTES: Why Meiosis?
NOTES: Stages of Meiosis

3. MEIOSIS
46 chromosomes
46 chromosomes
Essential Question: How does meiosis differ from mitosis and how does meiosis create cells that are genetically different from the parent cell?

4. 1) Somatic (body) cells EX: skin, brain, liver, etc
Two Types of Cells
1) Somatic (body) cells EX: skin, brain, liver, etc
2) Sex cells Ex: Cells in reproductive organs (testes & ovaries)
Meiosis occurs in sex cells

5. Meiosis Interphase I Prophase I Metaphase I Anaphase I Telophase I
Prophase II Metaphase II Anaphase II Telophase II

6. Meiosis takes place in two series of steps & includes TWO Divisions
Meiosis I I, P, M, A, T +
Meiosis II P, M, A, T
Which means…no DNA replication before meiosis II
No second Interphase

7. Stages of Meiosis

8. Interphase I
DNA replicates creating homologous chromosomes

9. 1) PROPHASE I
Homologous chromosomes pair up forming a tetrad (4 chromatids)
Images modified from:

10. Homologous chromosomes exchange DNA Creates genetic diversity
2. CROSSING OVER OCCURS
Homologous chromosomes exchange DNA
Creates genetic diversity

11. 2) Metaphase I
Tetrads line up in the middle

12. 3) Anaphase I- Tetrads pull apart

13. 4) Telophase I- Two new cells are formed

14. No Interphase II which means chromosomes are NOT copied again.
Meiosis II
No Interphase II which means chromosomes are NOT copied again.

15. 5) Prophase II ~ TWO cells begin meiosis II

16. 6) Metaphase II: chromosomes line up in the middle

17. 7) Anaphase II : chromosomes are pulled to opposite ends of the cell

18. 8) Telophase II / Cytokinesis ~ The two cells divide to form 4 genetically different cells (gametes)

19. End Result of Meiosis
Sex cells begin meiosis diploid (2 copies of each chromosome)
At the end of meiosis, four new cells (gametes)are formed

20. End Result of Meiosis
Gametes are haploid (half # chromosomes as parent cell)
Gametes will mature into sperm or eggs for sexual reproduction

21. Meiosis Video

22. What are the major differences between Mitosis and Meiosis?

23. Mitosis vs Meiosis Diploid Parent Cell Crossing over occurs
2 cell divisions
2 identical, diploid somatic cells
4 genetically different, haploid gametes

24. Mitosis Meiosis Body cells (Somatic) Sex cells (Gamete)
2 daughter cells same as parent cell (diploid – 2n)
4 daughter cells w/half chrom. (haploid – 1n)
Asexual reproduction
Sexual reproduction