1. BELL WORK Pick up the two note pages Get plickers card
Get out note page from Friday

2. Mrs. Stewart Biology I Stewarts Creek High School
MITOSIS VS. MEIOSIS
Mrs. Stewart
Biology I
Stewarts Creek High School

3. Objectives: Differentiate between the process of mitosis and meiosis
Demonstrate the movement of chromosomes throughout meiosis
Analyze how meiosis leads to genetic variation

4. Face Partners:

5. Review 2 ways for animals/cells to reproduce Asexual reproduction
Mitosis
Binary fission
These are used to create daughter cells that are identical to parent cells
Sexual reproduction
This creates daughter cells that are genetically different from parent

6. REVIEW: Cell Cycle Mitosis Interphase M-phase (mitosis) Cytokinesis
G1, S, and G2
M-phase (mitosis)
P-M-A-T
Cytokinesis
Mitosis
Asexual reproduction
Produces 2 identical daughter cells
Daughter cells are diploid
Daughter cells are identical to parent/mother cell

8. What differences can you see?
How many sets of chromosomes are in the cells that Meiosis produces?
How many cells does Meiosis produce?
How many divisions occur in Meiosis?

9. Final Products:
Mitosis
2 identical daughter cells
Somatic cells
Diploid
Meiosis
4 genetically different daughter cells
Gametes
Haploid

10. Mitosis vs. Meiosis Animation

11. Mikey: Explain to Raph how meiosis differs from mitosis

12. Why are gametes haploid?
Because two gametes fuse to create an offspring during sexual reproduction
Sperm (23) + Egg (23) = Offspring (46)

13. What happens in fertilization?
Fertilization of an egg
Zygote = the intial cell created from the fusion of a sperm and an egg

14. Fertilization to Implantation

15. Raph: summarize the process of fertilization for Mikey

16. Bell Work: Pick up the one note page up front
Copy down the process of binary fission in your class notebook

17. Review:
How do both Meiosis AND Mitosis play a role in the creation and development of a new organism?
Meiosis = creates the gametes used to fertilize/create the new organism
Mitosis = how the new organism grows and develops past the zygote stage

18. MEIOSIS:
The process of creating haploid gametes for sexual reproduction

19. Vocabulary Two categories for chromosomes:
Sex chromosomes (2 out of 46)
the 23rd pair
determine sex (gender)
Autosomes (44 out of 46) – all the rest

20. KARYOTYPES
A picture taken from a microscope of all the chromosomes within a cell.
The chromosomes are then arranged in homologous pairs and given a set of numbers

21. Karyotypes
Each homolog shares the same genes (the stripes) in the same location
NOTE: They do not have to have the same alleles

22. Homologous Chromosomes
Homologous chromosomes (homologs)
The two copies of each autosome
They are a matching pair
Which means they have the same genes, in the same location.
Where did they come from? Why do you have two?

23. Homologs come from mom and dad

24. Matching socks = Homologs

26. Mikey: Explain to Raph what a homologous chromosome pair is and where they came from.

27. How did babies get one homologue from each parent?
Meiosis
Creates haploid sex cells
Each sex cell has 23 chromosomes that are randomly assorted
This occurs through two cell divisions

28. Two Divisions:
Meiosis can reduce the amount of DNA within each daughter cell by dividing twice

29. What are the steps? Division One Division Two Interphase
Phases of Meiosis I
Prophase I
Metaphase I
Anaphase I
Telophase I
Cytokinesis
Interkinesis
Phases of Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Division One
Division Two

31. Let’s see it in action!
Meiosis animation

32. Interphase DNA replicates Makes the diploid (2n) cell now be (4n)
This process results in sister chromatids that will be attached by a centromere (X-shaped Chromosomes)

33. This karyotype shows homologous chromosome pairs right after cell division has occurred.

34. This karyotype shows homologs during prophase I after DNA replication has occurred
Note how each chromosome has two chromatids that are EXACT copies of each other

35. Prophase I Homologous chromosomes find each other and pair up
This is called forming a tetrad
Crossing over occurs
Chromatids MAY exchange portions of DNA

36. Bell Work
How does Prophase I contribute to genetic variation?

37. Why is crossing over so important?
Crossing over exchanges pieces of the chromatids. This will cause a new combination of alleles
This leads to genetic variation
Because the chromatids that are passed to the offspring may have a different combination of alleles than the original chromatids
This means that if a gamete that contains the newly combined chromatid is used to fertilize a zygote, then the baby will have a different combination of traits than the parent. = Variation!

38. Example: A = Can roll tongue, and a = cannot roll tongue
B = Freckles and b = no freckles
It is now possible for baby to be able to roll tongue and have NO freckles, which was never possible for original chromosomes

39. Prophase I Homologues (homologous pairs of chromsomes) form Tetrads
Crossing Over occurs

40. Raph: Explain to Mikey the difference between homologous chromosomes and a tetrad

41. Mikey: Explain to Raph the process of crossing over and how that leads to genetic variation

42. Telophase I and Cytokinesis
Metaphase I
Spindle fibers attach to the chromosomes
Tetrads line up in the middle of the cell
Anaphase I
Fibers pull the homologous chromosomes toward
opposite ends of the cell
Telophase I and Cytokinesis
Nuclear membranes form
Cell separates into two new cells

44. Interkinesis Resting period between Meiosis I and Meiosis II
DNA DOES NOT REPLICATE AGAIN HERE!

45. Meiosis II
The daughter cells from Meiosis I divide again WITHOUT replicating their chromosomes
That leads to 4 gametes, each with half the number of chromosomes (haploid) as the original “mother” cell

46. Telophase II and Cytokinesis
Prophase II
Spindle fibers form and move chromosomes to center
Metaphase II
Spindle fibers attach to the chromosomes
chromosomes line up in the middle of the cell – similar to how they do in Mitosis
Anaphase II
Fibers pull the sister chromatids toward
opposite ends of the cell
Telophase II and Cytokinesis
Nuclear membranes form
Both cells separate – forming 4 new haploid cells

49. How are the daughter cells genetically different?

50. Raphael: Walk Mikey through the whole process of meiosis

51. Genetic Variation
Sexual reproduction can lead to genetic variation between the offspring and the parents in 3 ways:
Crossing over – exchanging pieces of DNA leads to new DNA combinations on the chromosome
Random assortment of chromosomes – the parent’s homologues are randomly sorted into the gametes each time meiosis occurs
Random fertilization – which gametes combine to form baby is a random, unpredictable process

52. How is it that my daughter looks more like me but my son looks more like my husband?

53. Let’s see it in action!
Meiosis animation 1
Meiosis animation 2

54. Explanatory Videos Meiosis – Crossing Over
Random, Independent Assortment of Chromosomes

55. Bell work Each person: Pick up a copy of the meiosis pogil
Each table group: Pick up ONE white board, marker and eraser

56. Raph and Mikey together: Name two ways that meiosis leads to genetic variation

57. Oogenesis – meiosis in human female reproductive cells – makes eggs (ovum)
Total of 4 cells produced:
Occurs in the ovaries
Forms one usable egg cell with a large supply of stored nutrients.
The other 3 cells, called polar bodies, disintegrate.

58. Oogenesis

59. All 4 gametes produce a long whip-like tail
Spermatogenesis – meiosis in human male reproductive cells to make sperm (spermatazoa)
Occurs in the testes
Produces 4 viable sperm
All 4 gametes produce a long whip-like tail

60. Mikey: Explain to Raph why only one egg is usable but all 4 sperm are usable.

61. Meiosis: Cell division necessary for sexual reproduction
Produces 4 daughter cells
Daughter cells are Haploid
Daughter cells are gametes (sexual repro. cells)
2 nuclear/cellular divisions
Vital to maintain correct number of offspring in sexually reproducing organisms
Crossing over = opportunity for genetic variability

62. Differentiate Mitosis Meiosis Used for sexual reproduction
Produces 4 daughter cells
Daughter cells are Haploid
Daughter cells are genetically different from each other, and from parent cell
Produces gametes
Two nuclear/cellular divisions
Asexual reproduction
Produces 2 daughter cells
Daughter cells are diploid
Daughter cells are identical to each other and to parent cell
Produces somatic cells
One cell/nuclear division

63. Human chromosomal diseases
**Mistake in meiosis (called nondisjunction) can lead to an incorrect chromosomal number, causing consequences for offspring**
Down’s syndrome (extra chromosome #21)
Turner’s syndrome (missing or incomplete X chromosome in girls)
Klinefelter’s syndrome (males that have an extra X chromosome [XXY])

64. As a table group:
How does a baby with Down’s Syndrome end up with 3 chromosome #21s?

65. Video
Meiosis square dance

67. Meiosis Pogil Assign group roles Complete #1 – 4 5 minutes
RECORDERS: Share #4

68. Meiosis Pogil
Complete #5-8
5 minutes
RECORDERS: Share #8

69. Meiosis Pogil Complete #9-13 5 minutes
RECORDERS: Share #12 a, 12b, and 13

70. Bell work
If the cells produced at the end of Meiosis I are technically already haploid, then why is it necessary for them to divide again in Meiosis II?

71. Meiosis Pogil
Complete #
5 minutes
RECORDERS: Share #17 and 18

72. Independent (Random) Assortment Activity
Our cell has 13 pairs of chromosomes.
What is the diploid number?
Hint: How many chromosomes total are in our cell?
Key points:
The red cards represent chromosomes from mom
The black cards represent chromosomes from dad
The different suites do not matter in this activity

73. Meiosis Pogil
Complete #
7 minutes
RECORDERS: Share #21