1. Cell Division
--Meiosis--

2. Meiosis How does it differ from mitosis? Do all cells do it?
Why is it done?

3. The Cell Cycle

4. Mitosis
In mitosis, chromosomes are duplicated once and the cell divides once.
Each daughter cell has the same number of chromosomes as the parent cell.

5. Mitosis vs Meiosis
In mitosis, chromosomes are duplicated once and the cell divides once.
In meiosis, chromosomes are duplicated once and the cell divides twice.

6. Meiosis
In meiosis, chromosomes are duplicated once and the cell divides twice.
Each daughter cell has half the number of chromosomes as the parent cell.

7. Do all cells undergo meiosis?
NO!!
Only sex cells undergo meiosis
Why only sex cells?
So each sex cell (gamete) has the haploid (1n) number of chromosomes.
So each gamete has half the number of chromosomes.
Male gamete + femal gamete = zygote
1n n = 2n

8. Adult
Male 2n
Sexual Reproduction Cycle
Adult
Female 2n
gametes
meiosis
meiosis n n
zygote 2n
2n = diploid
n = haploid
mitosis
New
Adult 2n

9. PRACTICE n 2n Penicillium 1 Fruit flies 4 Gorillas 24 Pea plants 14
Goldfish 47
Some ferns
1000

10. PRACTICE n 2n Penicillium 1 2 Fruit flies 4 Gorillas 24 48 Pea plants7 14
Goldfish 47 94
Some ferns
500
1000

11. Where does meiosis occur?
Meiosis occurs in the reproductive structures and organs.
Meiosis occurs in the testes of the male and is called spermatogenesis.
Male gametes are sperm
Meiosis occurs in the ovaries of the female and is called oogenesis.
Female gametes are eggs

12. Gamete production in males (spermatogenesis)

13. Gamete production in females (oogenesis)

14. Where does meiosis occur?
Special cells in the reproductive structures called germ cells undergo meiosis
The germ cells produce haploid gametes
Eggs and sperm are haploid (1n) gametes
When gametes join, they produce a diploid (2n) zygote

15. Me I o s I s

16. Analogy
Imagine you have two sets of books on how to build a house; each set has 23 books.
One set was given to you by your mother; the other set by your father.
You must have all 46 books to build your house, even though you may not use all of the information in all the books.

17. Each set of books is analogous to the genetic material received from one parent.
One set is the information in the egg and one set is the information in the sperm.
Humans have 46 chromosomes; each gamete has 23 chromosomes.

18. Meiosis Prophase I Prophase II Meiosis consists of two stages:
MEIOSIS I & MEIOSIS II.
Prophase I Prophase II
Metaphase I Metaphase II
Anaphase I Anaphase II
Telophase I Telophase II

19. Meiosis 2n 2n Meiosis 1 End of Meiosis I n Meiosis II
End of Meiosis II n

20. Meiosis
Step by Step

21. Interphase
Meiosis I
Prophase I
Metaphase I
Anaphase I
Telophase I

22. Results of Meiosis I
At the beginning of Meiosis I there was one diploid cell.
At the end there are two haploid cells. 2n 1n

23. Meiosis II
The next set of cell divisions will separate the chromatids.
This process is very similar to the process of mitosis

24. Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II

25. Results of Meiosis II
At the beginning of meiosis II, there were 2 haploid cells
At the end of meiosis, 4 new haploid cells have been formed formed. 1n 1n

26. ONE diploid cell
prophase I (CROSSING-OVER OCCURS)
metaphase I
anaphase I
telophase I / cytokinesis
prophase II
metaphase II
anaphase II
telophase II
cytokinesis
FOUR haploid cells

27. Cell Division--Meiosis
End

28. Prophase I
Telophase I
Metaphase I
Anaphase I

29. Prophase II
Metaphase II
Anaphase II
Telophase II