1. Chapter 5 Part II: Meiosis

2. Learning Target
7. Recognize the type of daughter cells formed during meiosis and the chromosome number as compared to the parent cell. 9. Explain how meiosis and sexual reproduction increases genetic diversity

3. Meiosis Reduction division  reduces 2n cells to 1n cells
Two nuclear divisions  4 haploid daughter cells (no DNA replication after S phase)
Produces gametes
Homologous Chromosomes (Matching chromosomes  1 from Mom, 1 from Dad)
Two parts  Meiosis I and Meiosis II

4. Comparison of meiosis and mitosis
Fig 5.14

5. Meiosis I Similar to Mitosis Prophase I Metaphase I Anaphase I
Telophase I

6. Prophase I Exactly like Mitosis PLUS Synapsis Crossing-over
Homologous chromosomes pair up  form tetrads
Crossing-over
Tetrads wrap around each other & exchange DNA

7. Metaphase I
Tetrads pushed to center of cell

8. Anaphase I
Tetrads pulled apart to opposite sides of cell (chromatids are still joined at centromere)  separate independently (Independent Assortment)

9. Telophase I Reverse of Prophase I
Followed by Cytokinesis I (Interkinesis)

10. Cytokinesis I Interkinesis

11. Meiosis II
EXACTLY LIKE MITOSIS!!!

15. Results of Meiosis 1 cell (2n)  4 cells (1n) Genetic recombination
Genetic variability
Step-through animation

16. Benefits of Meiosis
Genetic variation  increases chances of survival !

17. Learning Check
8. How would you describe the daughter cells that come from Meiosis?
9. What are ways genetic diversity is increased in Meiosis? (3 ways)

18. Learning Targets
8. Explain how chromosomes are transmitted to the next generation via mitosis or meiosis followed by fertilization. 10. Compare and contrast spermatogenesis and oogenesis.

19. Human Life Cycle Fig 5.15 Requires both mitosis and meiosis
In females meiosis is part of the process of oogenesis
In males meiosis is part of spermatogenesis
At fertilization, the resulting zygote divides by mitosis for the processes of growth and development
Mitosis is used for repair throughout life
Fig 5.15

20. Spermatogenesis 1 Primary spermatocyte (2n) 
2 Secondary spermatocytes (1n) 
4 spermatids (1n) 
4 sperm cells
Begins at puberty and continues throughout life

21. Oogenesis Begins before birth with Meiosis I
proceeds to Meiosis II
STOPS at Metaphase II
Primary oocyte (2n)
Secondary oocyte (1n) + polar body (1n) (enters fallopian tube)
If fertilization occurs, Meiosis II proceeds & 2o oocyte  egg & polar body
Benefit: 1 egg gets almost all the cytoplasm
Why?

22. Spermatogenesis and oogenesis

23. Comparison of meiosis and mitosis
Fig 5.14

24. Learning Target
11. Describe the role of programmed cell death in development.

25. Cell Death… Apoptosis…but why?
Allows body to absorb nutrients from those cells

26. Learning Targets
12. Determine sex and chromosomal abnormalities from a karyotype.

27. Human Karyotypes How many chromosomes do humans have?
23 PAIRS!
A male genotype is: XY
A Female genotypes is: XX

28. Learning Check!
Gender?
Abnormalities?

29. Learning Check!
Gender?
Abnormalities?