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

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

3. Face Partners:

4. 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

5. 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

7. 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?

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

9. Mitosis vs. Meiosis Animation

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

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

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

13. Fertilization to Implantation

14. Raph: summarize the process of fertilization for Mikey

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

16. 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
Homologous chromosomes (homologues)
The two copies of each autosome
Where did they come from?

17. Homologues come from mom and dad

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

19. 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

20. What are the steps? Phases of Meiosis I Interkinesis
Prophase I
Metaphase I
Anaphase I
Telophase I
Cytokinesis
Interkinesis
Phases of Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II

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

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

24. Here is a karyotype showing homologous chromosome pairs

25. Here is a karyotype after DNA replication has occurred
Notice how each chromosome has duplicated itself.

26. Prophase I
Homologous chromosomes pair up (forming a tetrad) - Mom & Dad go on a date
Crossing over occurs
Chromatids MAY exchange portions of DNA
Leads to genetic variances

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

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

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

30. 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

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

33. 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

34. 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

37. How are the daughter cells genetically different?

38. 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

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

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

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

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

43. 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.

44. Oogenesis

45. 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

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

47. 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

48. 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

49. Human chromosomal diseases
**Mistake in meiosis 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])

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

51. Video
Meiosis square dance