1. Before we start….
Mitosis gif

2. Topic 1.3: How do living things sexually reproduce?

3. Concept 1: Male and reproductive cells combine to produce a zygote
Sexual reproduction requires two parents, each contributing a sex cell called a gamete

4. Concept 1: Male and reproductive cells combine to produce a zygote
Sexual reproduction requires two parents, each contributing a sex cell called a gamete
The male contributes sperm cells

5. Concept 1: Male and reproductive cells combine to produce a zygote
Sexual reproduction requires two parents, each contributing a sex cell called a gamete
The male contributes sperm cells
The female contributes an egg cell (also known as an ovum)

6. Concept 1: Male and reproductive cells combine to produce a zygote
Sexual reproduction requires two parents, each contributing a sex cell called a gamete
The male contributes sperm cells
The female contributes an egg cell (also known as an ovum)
When the male and female gametes combine, fertilization occurs.

7. Concept 1: Male and reproductive cells combine to produce a zygote
Sexual reproduction requires two parents, each contributing a sex cell called a gamete
The male contributes sperm cells
The female contributes an egg cell (also known as an ovum)
When the male and female gametes combine, fertilization occurs.

8. Concept 2: reproductive cells are formed by a cell-dividing process called meiosis
Although human cells have 46 chromosomes, each chromosome is not unique

9. Concept 2: reproductive cells are formed by a cell-dividing process called meiosis
Although human cells have 46 chromosomes, each chromosome is not unique
Each chromosomes has a pair that carries almost identical information, called an homologous pair

10. Concept 2: reproductive cells are formed by a cell-dividing process called meiosis
Although human cells have 46 chromosomes, each chromosome is not unique
Each chromosomes has a pair that carries almost identical information, called an homologous pair
One chromosome comes from the mother

11. Concept 2: reproductive cells are formed by a cell-dividing process called meiosis
Although human cells have 46 chromosomes, each chromosome is not unique
Each chromosomes has a pair that carries almost identical information, called an homologous pair
One chromosome comes from the mother
One chromosome comes from the father

12. Concept 2: reproductive cells are formed by a cell-dividing process called meiosis
Although human cells have 46 chromosomes, each chromosome is not unique
Each chromosomes has a pair that carries almost identical information, called an homologous pair
One chromosome comes from the mother
One chromosome comes from the father
Human cells have 23 homologous pairs

15. Homologous pair

18. Down Syndrome

19. Diploid Haploid What is the goal of meiosis? Type of cell:
Type of cell:
Number of chromosomes (in a human cell)
Number of copies of each chromosome
Formed through:
Diploid
Haploid
What is the goal of meiosis?

20. Diploid Haploid What is the goal of meiosis? Type of cell:
Type of cell:
Number of chromosomes (in a human cell)
Number of copies of each chromosome
Formed through:
Diploid
Haploid
What is the goal of meiosis?

21. 46 Diploid Haploid What is the goal of meiosis? Type of cell:
Type of cell:
Number of chromosomes (in a human cell)
Number of copies of each chromosome
Formed through:
Diploid 46
Haploid
What is the goal of meiosis?

22. 46 2 Diploid Haploid What is the goal of meiosis? Type of cell:
Type of cell:
Number of chromosomes (in a human cell)
Number of copies of each chromosome
Formed through:
Diploid 46 2
Haploid
What is the goal of meiosis?

23. 46 2 Mitosis Diploid Haploid What is the goal of meiosis?
Type of cell:
Number of chromosomes (in a human cell)
Number of copies of each chromosome
Formed through:
Diploid 46 2
Mitosis
Haploid
What is the goal of meiosis?

24. 46 2 Mitosis Diploid Haploid What is the goal of meiosis?
Type of cell:
Number of chromosomes (in a human cell)
Number of copies of each chromosome
Formed through:
Diploid 46 2
Mitosis
Haploid
What is the goal of meiosis?

25. 46 2 Mitosis 23 Diploid Haploid What is the goal of meiosis?
Type of cell:
Number of chromosomes (in a human cell)
Number of copies of each chromosome
Formed through:
Diploid 46 2
Mitosis
Haploid 23
What is the goal of meiosis?

26. 46 2 Mitosis 23 1 Diploid Haploid What is the goal of meiosis?
Type of cell:
Number of chromosomes (in a human cell)
Number of copies of each chromosome
Formed through:
Diploid 46 2
Mitosis
Haploid 23 1
What is the goal of meiosis?

27. 46 2 Mitosis 23 1 Meiosis Diploid Haploid What is the goal of meiosis?
Type of cell:
Number of chromosomes (in a human cell)
Number of copies of each chromosome
Formed through:
Diploid 46 2
Mitosis
Haploid 23 1
Meiosis
What is the goal of meiosis?

28. 46 2 Mitosis 23 1 Meiosis Diploid Haploid What is the goal of meiosis?
Type of cell:
Number of chromosomes (in a human cell)
Number of copies of each chromosome
Formed through:
Diploid 46 2
Mitosis
Haploid 23 1
Meiosis
What is the goal of meiosis?
 To turn diploid cells into haploid cells.

29. Meiosis
Watch meiosis video

30. Interphase
DNA is replicated
Organelles are replicated
Cell grows

31. Interphase DNA is replicated Organelles are replicated Cell grows
Prepare to divide

32. Enter Meiosis I….

33. Prophase I Nuclear membrane disappears DNA condenses into chromosomes
Homologous chromosomes pair up

34. Prophase I Nuclear membrane disappears DNA condenses into chromosomes
Homologous chromosomes pair up
One diploid cell
Duplicated DNA

35. Metaphase I Spindle fibers attach to chromosomes
Chromosomes line up along the middle of the cell

36. Metaphase I Spindle fibers attach to chromosomes
Chromosomes line up along the middle of the cell
One diploid cell
Duplicated DNA

37. Anaphase I
Homologous chromosomes separate and move to each end of the cell

38. Anaphase I
Homologous chromosomes separate and move to each end of the cell
One diploid cell
Duplicated DNA

39. Telophase I
Two nuclei form and each nucleus contains a complete copy of the cell’s DNA
Cell is ready to divide

40. Telophase I
Two nuclei form and each nucleus contains a complete copy of the cell’s DNA
Cell is ready to divide
One diploid cell
Duplicated DNA

41. Cytokinesis
Cell divides into two cells

42. Cytokinesis Cell divides into two cells Two haploid cells
Duplicated DNA

43. Enter meiosis II…

44. Prophase II
Nuclear membranes disappear

45. Prophase II Nuclear membranes disappear Two haploid cells
Duplicated DNA

46. Metaphase II
Chromosomes line up single file along the middle of the cell

47. Metaphase II
Chromosomes line up single file along the middle of the cell
Two haploid cells
Duplicated DNA

48. Anaphase II
Duplicated chromosomes are pulled apart and one copy moves to each end of the cell

49. Anaphase II
Duplicated chromosomes are pulled apart and one copy moves to each end of the cell
Two haploid cells
Duplicated DNA is separated

50. Telophase II
Four nuclei form
Cell prepares to divide

51. Telophase II Four nuclei form Cell prepares to divide
Two haploid cells
Duplicated DNA is separated

52. Cytokinesis
Two cells divide into four cells

53. Cytokinesis Two cells divide into four cells Four haploid cells
One copy of DNA

55. Variation and Diversity
Sexual reproduction introduces diversity during meiosis in two main ways

56. Variation and Diversity
Sexual reproduction introduces diversity during meiosis in two main ways
Crossing over: occurs during prophase I when the legs of two homologous chromosomes cross over and exchange genetic material

57. Crossing over

58. Variation and Diversity
Sexual reproduction introduces diversity during meiosis in two main ways
Crossing over: occurs during prophase I when the legs of two homologous chromosomes cross over and exchange genetic material

59. Variation and Diversity
Sexual reproduction introduces diversity during meiosis in two main ways
Crossing over: occurs during prophase I when the legs of two homologous chromosomes cross over and exchange genetic material
Independent assortment: during metaphase I the homologous pairs line up randomly, resulting in a random combination of chromosomes in each gamete cell

60. Variation and Diversity
Sexual reproduction introduces diversity during meiosis in two main ways
Crossing over: occurs during prophase I when the legs of two homologous chromosomes cross over and exchange genetic material
Independent assortment: during metaphase I the homologous pairs line up randomly, resulting in a random combination of chromosomes in each gamete cell

61. Independent assortment

62. Meiosis versus Mitosis