1. Meiosis
Catalyst:
How many DIFFERENT TYPES of chromosomes do human somatic cells have?
How many COPIES OF EACH TYPE of chromosome do human somatic cells have?
Write in complete sentences!
Don’t talk during the Catalyst!

2. By the end of today, SWBAT…
Objectives
By the end of today, SWBAT…
Describe the phases and products of meiosis

3. Let’s look at Mitosis one more time.
Draw on whiteboard, 23 types of chromosome, two of each type = 2N
During interphase, doubling  23 types of chromosomes, four of each type = 4N
During telophase, cell splits  23 types of chromosomes, two of each type = 2N

4. Review and Vocabulary
Human cells have 23 different types of chromosome
Mitosis produces cells that are 2N. Another word for this is diploid.
Diploid = 2 copies of each type of chromosome
Meiosis produces cells that are 1N. Another word for this is haploid.
Haploid = 1 copy of each type of chromosome
Draw on whiteboard. 23 different types of chromosome, 2 of each type.

5. Why? 2N 4N Key Point #1: Gametes must be haploid (1N)
Every human must have two copies of each chromosome
If gametes were diploid (2N), the child would not survive
2N is the regular number of chromosomes!
You don’t want a baby with 4N!!!!!! 2N 1N
How do we get haploid cells? Well, in meiosis… cells divide TWICE! 2N 4N 2N N

6. Key Point #2: In meiosis, gametes divide twice.
Meiosis is the process of gamete cell division. It is used for sexual reproduction.
Key Point #2: In meiosis, gametes divide twice.
Produces four cells
Each cell is haploid (1N)

7. Meiosis 2N 2N In meiosis, there are two rounds of cell division 2N→4N
MEIOSIS I
MEIOSIS II 1N 2N 1N 1N
The starting 2N cell is a germ cell; it produces gametes. Germ cells are the only cells in the body that undergo both mitosis (to create more germ cells) and meiosis (to create gametes). 2N 1N

8. Family Matters Meiosis can explain a lot of things in life…
Especially the age-old question…
Why am I look so much better looking than my sister, even though we have the same parents?
So if gametes need to be haploid, not diploid, then they can’t divide via mitosis. They have to divide through meiosis.

9. Thank you, meiosis!

10. Germ Cell in Interphase
Meiosis
Key Point #3: Meiosis produces genetically DIFFERENT cells.
Why different? Genetic information between chromosomes gets switched.
Analogous parts of the chromosomes get switched. So the reason my sister and I look different is she came from eggs/sperm that are DIFFERENT than the ones I came from.
Germ Cell in Interphase
Prophase I
Metaphase I
Anaphase I
Telophase I

11. More Meiosis
Telophase II
Anaphase II
Prophase II
Metaphase II

12. A Closer Look 4N 1N 1N 1N 1N
Use this page to show them that the original 2N cell has twice as much DNA as each of the 4 products of meiosis.

13. Take a step back Can someone tell me what mitosis is for?
Can someone tell me what meiosis is for?
What’s the difference between haploid and diploid?
Why is it important that gametes are haploid?
Student voices!!!

14. ActivExpression Practice!

15. Meiosis produces… Identical cells Different cells 23 types of cells
Guided Practice
Meiosis produces…
Identical cells
Different cells
23 types of cells
Two copies of each cell

16. Meiosis occurs in… Somatic cells Gametes Chromosomes
Guided Practice
Meiosis occurs in…
Somatic cells
Gametes
Chromosomes
All eukyarotic cells

17. How many times do cells divide in meiosis? 1 2 3 4
Guided Practice
How many times do cells divide in meiosis? 1 2 3 4

18. Guided Practice
The cells produced by meiosis are _____, also known as ______.
Haploid… 1N
Diploid… 1N
Haploid… 2N
Diploid… 2N

19. Guided Practice
Gametes have _____ copy/copies of each type of chromosome. 1 2 23 46

20. Guided Practice What would happen if gametes were 2N?
Children would be 2N, and die
Children would be 4N, and have superpowers
Children would be 4N, and die
Trick question, gametes are 2N!

21. Were You Paying Attention?
I’m going to ask the same questions again! Answers are scrambled

22. Meiosis produces… Different cells Two copies of each cell
Guided Practice
Meiosis produces…
Different cells
Two copies of each cell
Identical cells
23 types of cells

23. Meiosis occurs in… Chromosomes Somatic cells All eukyarotic cells
Guided Practice
Meiosis occurs in…
Chromosomes
Somatic cells
All eukyarotic cells
Gametes

24. How many times do cells divide in meiosis? 4 3 2 1
Guided Practice
How many times do cells divide in meiosis? 4 3 2 1

25. Guided Practice
The cells produced by meiosis are _____, also known as ______.
Haploid… 1N
Haploid… 2N
Diploid… 1N
Diploid… 2N

26. Guided Practice
Gametes have _____ copy/copies of each type of chromosome. 2 46 23 1

27. Guided Practice What would happen if gametes were 2N?
Children would be 4N, and die
Children would be 4N, and have superpowers
Trick question, gametes are 2N!
Children would be 2N, and die

28. So far, we’ve only been talking about meiosis
Step Yo’ Game Up!
So far, we’ve only been talking about meiosis
On the test, you will have to COMPARE meiosis and mitosis

29. Produces cells with 2N chromosomes
Guided Practice
Produces cells with 2N chromosomes
Mitosis
Meiosis

30. Guided Practice
Creates diploid cells
Mitosis
Meiosis

31. Produces four DIFFERENT daughter cells
Guided Practice
Produces four DIFFERENT daughter cells
Mitosis
Meiosis

32. Creates cells with 1N chromosomes
Guided Practice
Creates cells with 1N chromosomes
Mitosis
Meiosis

33. Genetic information between chromosomes gets switched
Guided Practice
Genetic information between chromosomes gets switched
Mitosis
Meiosis

34. Guided Practice Which of the following is true?
There are more cell divisions in mitosis than meiosis
There are more cell divisions in meiosis than mitosis
There are the same number of cell divisions in both
The cell does not divide in mitosis or meiosis
1 in mitosis, 2 in meiosis

35. Guided Practice Mitosis occurs in _____, meiosis occurs in _____
Animals… Animals and plants
Gametes… somatic cells
Eukaryotic cells… prokaryotic cells
Somatic cells… gametes

36. Guided Practice
Mitosis produces _____ cells, meiosis produces _____ cells.
Haploid… diploid
Gametes… somatic
Eukaryotic… prokaryotic
1N… 2N

37. Independent Practice/HW
Lately, my lessons have been running short, and students have had time to pretty much finish homework in class. They should not, today.

38. Key Point Wrap-Up Key Point #1: Gametes must be haploid (1N)
Meiosis is the process of gamete cell division. It is used for sexual reproduction.
Key Point #2: In meiosis, gametes divide twice.
Key Point #3: Meiosis produces genetically DIFFERENT cells.

39. Exit Questions What is the purpose of meiosis?
How many cells does meiosis produce?
Why is Mr. J so much better looking than his sister? (Hint: it has to do with sperm and egg cells.)
Write in complete sentences!
Don’t talk during the Catalyst!

40. The following slides are extension
Will not be tested; only if students are curious

41. Women only produce one viable egg in meiosis, the other three cells are polar bodies that will be destroyed.
Women only produce a few hundred eggs over the course of their entire lives.
extension
Oogenesis

42. Men are busy – meiosis produces roughly 250,000,000 sperm per day!!!
extension
Spermatogenesis