1. DO NOW!!! F, T, T True or False:
The offspring of sexual reproduction have fewer chromosomes than their parents have.
Sex cells are produced by cell division.
During sexual reproduction, two cells combine to form a new organism.
F, T, T

2. Meiosis
Unit 2 Lesson 2

3. 2 Types of Cells in Body
Sex Cells – have half the genetic information - 23 chromosomes = Haploid 1n
Body Cells – have genetic information - 46 chromosomes = Diploid 2n

5. Body cells - 46 chromosomes = 23 pairs – homologous pairs Sex cells - 23 chromosomes - no homologous pairs.
Cell

6. Homologous Chromosomes
Body cells – 23 homologous pairs
Homologous chromosomes - carry genes for same trait.
Some - different versions of same trait.
Example: Trait for hair color – black, red, blond hair, etc. 6

7. homologous chromosomes
Came From
Mother
Came from
Father

8. Chromosome pair #23 - sex chromosomes -control sexual characteristics.
Sex cells – Gametes
Female gametes = egg
Male gametes = sperm
XX = Female
XY = Male
Cell
So humans have two chromosomes number 1’s, 2 chromosomes number 2’s ect. all the way down to 23. So that is what a homologous chromosomes. Homologous chromosomes carry genes for the same traits. Chromosome pair 23 are the sex chromosomes because they control the sex of the individual.

10. Sex cells
Sex cells - half genetic information - 23 chromosomes (1 of each pair) – Haploid 1n
After sexual reproduction – 2 sex cells combine - offspring has 46 chromosomes = 2 of each pair – Diploid 2n 10

11. = 1n
23 Chromosomes
= 2n
46 Chromosomes
= 1n
23 Chromosomes

12. Meiosis
Type of cell division - produces haploid sex cells - sperm & egg cells
Where? – Reproductive organs of males and females
Starts - 1 cell - 46 chromosomes – 23 homologous pairs – 2n Diploid
Ends - 4 cells - each have 23 chromosomes – 1 of each pair – 1n Haploid 12

13. HW
Read page 102 and 103 and complete questions #5 - 7

14. DO NOW Quiz!!! How many chromosomes do body cells have?
How many chromosomes do sex cells have?
Sex cells are called _____________ ?
What is the difference between diploid and haploid?

15. DO NOW QUIZ ANSWERS!!! 46 23 Gametes
Diploid has 46 chromosomes (23 pairs) and haploid has 23 chromosomes (only one set of the diploid pair)

16. Meiosis
Type of cell division - produces haploid sex cells - sperm & egg cells
Where? – Reproductive organs of males and females
Starts - 1 cell - 46 chromosomes – 23 homologous pairs – 2n Diploid
Ends - 4 cells - each have 23 chromosomes – 1 of each pair – 1n Haploid 16

17. homologous chromosomes
Came From
Mother
Came from
Father

18. Purpose of Meiosis Enable Reproduction
Conserve chromosome # in a species

19. Stages of Meiosis
2 parts:
Meiosis I
Meiosis II. 19

20. Cell

21. Before Meiosis I
During interphase - each homologous chromosome pair duplicates 21

22. homologous chromosomes
Came From
Mother
Came from
Father
Duplicated Chromosomes

24. Meiosis I vs Meiosis II
Meiosis I = duplicated homologous chromosomes separate.
Form 2 cells with 23 duplicated chromosomes (1 set of each homologous pair)
Meiosis II - sister chromatids separate.

25. Prophase I
Duplicated homologous chromosomes pair up. (1 & 1), (2 & 2), etc., all the way to (23 & 23)
1 & 1
2 & 2 25

26. Metaphase I
Duplicated homologous chromosome pairs - line up in the middle of the cell.
1 & 1
2 & 2 26

27. Anaphase I 1 & 1 2 & 2 23 duplicated chromosomes
Duplicated homologous chromosomes pairs - separate and move to opposite ends of cell
1 & 1
So if I have 23 duplicated chromosomes doesn't that mean I have 46 chromosomes? No, No, No, because the duplicated chromosomes are connected at the centromere, they are considered one duplicated chromosome. Only once they separate at the centromere do they become two chromosomes. Chromatids are connected at the centromere, when the centromere splits, the chromatids become chromosomes.
2 & 2
23 duplicated chromosomes 27

28. Telophase I and Cytokinesis
Nuclear membranes re-forms – cell divides into 2 cells
23 duplicated chromosomes
23 duplicated chromosomes
Chromatids still attached 28

30. HW
Read Page 104 and 105 and complete questions # 8, 9, & 11

31. DO NOW Quiz!!! Where in the body does Meiosis Occur?
What is the purpose of Meiosis?
What is each half of a duplicated chromosome called?
What separated during Meiosis I?

32. DO NOW QUIZ ANSWERS!!! Reproductive organs of males and females.
Enable reproduction and conserve chromosome # in species.
Sister chromatid.
Duplicated Homologous Chromosomes separated.

33. Meiosis II
Meiosis I – created 2 cells – each has 23 duplicated chromosomes.
Meiosis II - 2 cells divide again - sister chromatids separate
End - 4 haploid sex cells 33

34. Meiosis II 4 sex cells all haploid 1n:
Males - develop into 4 sperm cells.
Females – develop into 1 egg cell
Females - 3 sex cells - break down & one sex cell becomes an egg – haploid 1n 34

35. Prophase II 23 duplicated chromosomes Nuclear membrane breaks apart.35

36. Metaphase II 23 duplicated chromosomes
Duplicated chromosomes line up in the middle of each cell.
23 duplicated chromosomes 36

37. Anaphase II . 23 chromosomes
Duplicated chromosomes sister chromatids -pulled apart and move to opposite sides.
23 chromosomes 37

38. Telophase II and Cytokinesis
Nuclear membranes re-form – 2 cells divide into 4 – each cell is haploid 1n – 23 chromosomes 38

40. Activity + HW
Draw the phases of Meiosis I and Meiosis II on a piece of paper and label each step in the process.

41. DO Now !!!
Read page 106 and complete the table.

42. Meiosis vs Mitosis Mitosis: Creates body cells
Chromosomes duplicated once
nucleus divides once
creates 2 identical Diploid 2n cells
Each have 46 chromosomes – 23 homologous pairs
Meiosis:
Creates sex cells
23 homologous chromosome pairs duplicated once
nucleus divides twice
creates 4 Haploid 1n sex cells
Each have 23 chromosomes – 1 of each pair 42

43. 4 Haploid 1n Cells = 23 chromosomes each
2 Diploid 2n cells
= 46 chromosomes each

44. Meiosis Video
0fIyFlY

45. Down Syndrome Down syndrome - genetic disease - error during meiosis.
Chromatids in chromosome 21 - do not separate - one sex cells gets an extra copy of chromosome 21.
Causes a number of health problems and learning difficulties - many people with Down syndrome have fulfilling lives. 45

47. Activity Compare your Meiosis drawings with a partner in the class.
Explain the process of your picture to your partner.
Correct mistakes and learn from one another.

48. HW
Complete the Lesson 2 Review on Page 109.