1. Unit 5
Mitosis & Meiosis

2. Why do cells divide rather than grow bigger?
Have you ever been in a traffic jam in a small town?
Where are major traffic jams found?
As a city’s population grows, more people are moving in an out which causes traffic
Cells are like cities
The bigger they are, the more food, water, and waste that must move in and out to keep the cell alive.

3. Why do cells divide rather than grow bigger?
To prevent traffic jams, they will divide
Cells divide for 4 major reasons:
1. Prevent the cell from becoming too big (prevent traffic jam)
2. To heal injuries
3. To allow the organism to grow (up)
4. To reproduce (new individuals)

4. Before we get started with the cell cycle…. Lets talk about chromosomes
Chromosome: DNA-containing structure that carries genetic material from one generation to another.

5. What happens during the cell cycle?
Cell Cycle - Process of cellular reproduction, occurring in the main stages
Interphase (growth)
Mitosis (nuclear division)
Cytokinesis (cytoplasm division)

6. What occurs during Interphase (the 1st step in cell cycle)
There are 3 stages during interphase:
1st Grows
2nd Duplicates DNA 46
Chromosomes 92
Chromosomes
3rd Prepares to divide

7. Which of the following is NOT a reason cells divide?
Clicker Question #1
Which of the following is NOT a reason cells divide?
To heal injuries
To allow the organism to grow
To reproduce
To maintain homeostasis

8. What will happen if the cell continued to grow rather than divide?
Clicker Question #2
What will happen if the cell continued to grow rather than divide?
The organism would get too big
Food & wastes would not be able to move in & out as easily
The surface area would increase and allow more materials into and out of the cell
Nothing would happen

9. What are the 3 stages of the cell cycle?
Clicker Question #3
What are the 3 stages of the cell cycle?
Prophase, Metaphase, & Anaphase
Mitosis, Telophase, & Cytokinesis
Interphase, Metaphase, & Prophase
Interphase, Mitosis, & Cytokinesis

10. Which of the following is NOT a stage during interphase?
Clicker Question #4
Which of the following is NOT a stage during interphase?
Growth (G1)
DNA replicates (S)
Prepares to divide (G2)
Mitosis (M)

11. What is Mitosis?
Mitosis: 2nd main stage of the cell cycle during which the cell’s replicated DNA divides and 2 genetically identical diploid daughter cells are produced.

12. What occurs during mitosis? (the 2nd step in cell cycle)
There are 4 stages during mitosis:
1st Prophase (pro = 1st)
2nd Metaphase
3rd Anaphase
4th Telophase (telo = end)

13. What occurs during mitosis? (the 2nd step in cell cycle)
There are 4 stages during mitosis:
1st Prophase (pro = 1st)
Nucleus disappears
Centrioles separate

14. What occurs during mitosis? (the 2nd step in cell cycle)
There are 4 stages during mitosis:
2nd Metaphase
Chromosomes line up in the middle

15. What occurs during mitosis? (the 2nd step in cell cycle)
There are 4 stages during mitosis:
3rd Anaphase
Chromosomes move apart

16. What occurs during mitosis? (the 2nd step in cell cycle)
There are 4 stages during mitosis:
4th Telophase (telo = end)
Nucleus reappears
Cytoplasm starts to separate

17. What occurs during cytokinesis? (the 3rd step (LAST) in cell cycle)
Cytokinesis: The last stage of the cell cycle, during which the cell’s cytoplasm divides, creating a new cell.
Daughter Cells

18. Clicker Question #5 Mitosis creates: 4 genetically identical cells
4 genetically different cells
2 genetically different cells

19. What are the 4 stages of mitosis in order?
Clicker Question #6
What are the 4 stages of mitosis in order?
Interphase, prophase, metaphase, anaphase
Interphase, prophase, metaphase, telophase
Prophase, metaphase, telophase, cytokinesis
Prophase, metaphase, anaphase, telophase

20. Clicker Question #7 Cytokinesis Interphase Telophase Metaphase
This is the last phase of the cell cycle where the cell’s cytoplasm divides to create 2 daughter cells:
Cytokinesis
Interphase
Telophase
Metaphase

21. Now, lets look at the difference between gametes & body cells.

22. What is the difference between gametes & body cells?
Gametes – A haploid sex cell, formed during meiosis, that can combine with another haploid sex cell and produce a diploid fertilized egg.
Sperm & Egg are gametes!
How many chromosomes are in human gametes? 23

23. What is the difference between gametes & body cells?
What are “body cells”?
Does more chromosomes an organism has mean that it is more advanced/smarter?
Brain cells Eye cells
Heart cells Tongue cells
Skin cells Muscle cells
Blood cells Lung cells
Kidney cells Nerve cells
Everything EXCEPT
GAMETES!
No…example:
Turkeys have 82 chromosomes in each cell
No…example:
King Crabs have 208 chromosomes in each cell
How many chromosomes do we have in each of our body cells (not sex cells)?
Humans have 46 in our body cells

24. Body cells reproduce using mitosis.
Start with 1 diploid
Notice that they are IDENTICAL!
End with 2 diploid

25. What is the difference between diploid and haploid?
Diploid – Having two copies of each chromosomes (2n)
Body cells are Diploid
If you see Diploid…
Fruit flies have 8
Skunks have 50
Humans have 46
You think DOUBLE!

26. Diploid Video

27. You think HALF! If you see haploid… Gametes are Haploid
What is the difference between diploid and haploid?
Haploid – Cell with half the number of chromosomes (n)
Gametes are Haploid 23 23 23 23
If you see haploid…
Humans have 23 (in sex cells)
Remember: Humans have 46 (in body cells)
Skunks have 25 (in sex cells)
Remember: Skunks have 50 in body cells
Fruit flies have 4 (in sex cells)
Remember: Fruit Flies have 8 in body cells
You think HALF!

28. Haploid Video

29. Sperm and eggs are: gametes somatic cells body cells all of the above
Clicker Question #8
Sperm and eggs are:
gametes
somatic cells
body cells
all of the above

30. How many chromosomes are in human gametes? 36 23 20 15
Clicker Question #9
How many chromosomes are in human gametes? 36 23 20 15

31. Which of the following is an example of a haploid cell?
Clicker Question #10
Which of the following is an example of a haploid cell?
brain cell
skin cell
heart cell
sperm cell

32. Clicker Question #11 Mitosis results in: 2 diploid cells
2 haploid cells
4 diploid cells
4 haploid cells

33. Gametes are formed using meiosis
Starts with 1 diploid
Notice that they are NOT IDENTICAL
Ends with 4 DIFFERENT haploid

34. What happens during Meiosis?
Meiosis: Reduction division process, occurring only in reproductive cells, in which 1 diploid (2n) cells produce 4 haploid (n) cells that are NOT genetically identical.
Creates EGGS inside the ovaries of females
Creates SPERM inside the testes of males

35. What happens during Meiosis?
There are 2 stages during Meiosis:
Meiosis I & Meiosis II
Meiosis I is exactly like mitosis EXCEPT that
Crossing-over occurs during prophase I

36. What happens during Meiosis?
Crossing-over: Exchange of chromosomal segments between a pair of homologous chromosomes during prophase I of meiosis
Meiosis I
Meiosis II

37. Why is crossing-over so important? (cuz it is)
It creates genetic variation!
Even though you look similar to your siblings (if same parents), there will never be another person exactly like you because of crossing-over…your parents could have a million kids, and not one of them will look exactly like you!
(except for identical twins, but even they have some differences)
Genetic variation allows some individuals to:
* Run faster than you
* “Look better” than you
* Fix things better than you
* Paint better than you
* Solve math problems better than you
* Sing better than you
* Train animals better than you
* Farm better than you
* Fly airplanes better than you
* Dance better than you
* Swim better than you
* Jump better than you

38. Crossing-Over Continued…
Crossing-over occurs between homologous chromosomes.
Homo means ___?
The same crossing-over patterns do not occur…they create all different kinds of combinations…often called “recombination”…this makes us genetically unique.
SAME
Homologous Chromosomes means that they contain the SAME genes, in the SAME order as each other, but the message in the genes may be slightly different between the two.
- So your mom’s code could be for blue eyes
- And your dad’s code could be for brown
Being genetically unique creates genetic diversity!
…diversity is GOOOOD!
Genetic diversity allows some individuals of the same species to continue as their environment changes…even if others can’t survive.

39. Hypothetical….lets say you are a duck…
And shaking your tail feathers will help you find a mate…
cuz that is what the ladyz are look’n for
Then this is the duck that will pass on his genes!

40. Hypothetical…lets say you are a caveman
Which of these would be LESS likely to survive?
Because all these cave people have genetic diversity, but one lacks an important trait (ability to build tools), he will not survive his environment… but the others will!

41. What happens during Meiosis?
Next is Meiosis II….
* The division process happens again…BUT
Meiosis I
The DNA does NOT copy before dividing
&
No crossing-over
Meiosis II
Results in 4 haploid cells that are NOT identical

42. Which of the following cells are formed during meiosis?
Clicker Question #12
Which of the following cells are formed during meiosis?
skin cells
liver cells
egg cells
kidney cells

43. Which of the following cells are formed during mitosis?
Clicker Question #13
Which of the following cells are formed during mitosis?
skin cells
sperm cells
egg cells
all of the above

44. Clicker Question #14 Meiosis results in: 2 identical haploid cells
4 different haploid cells
2 different haploid cells

45. Clicker Question #15 identical twins cloning genetic variation
This allows some individuals of the same species to continue as their environment change even if others can’t survive
identical twins
cloning
genetic variation
biodiversity

46. The exchange of chromosomal segments during meiosis is called:
Clicker Question #16
The exchange of chromosomal segments during meiosis is called:
interphase
crossing-over
transcription
exchanging-over

47. Which of the following allows for genetic diversity?
Clicker Question #17
Which of the following allows for genetic diversity?
meiosis
mitosis
homeostasis
all of the above

48. Houston…We have a problem…
Non-disjunction: Cell division in which the sister chromatids do NOT separate correctly, resulting in gametes with an abnormal number of chromosomes.
This is how Down Syndrome happens…the chromosomes don’t separate correctly, and too many end up in the gamete.
People with Down Syndrome have 47 chromosomes instead of ____.
These are correct!
No problem
Notice there are NO chromosomes in these cells!
Notice that non-disjunction occurred here too! 46

49. Click on Link for animation…
Meiosis Overview

50. Compare & Contrast Mitosis & Meiosis
Page 35 in Comp Book
Compare & Contrast Mitosis & Meiosis
Mitosis
Meiosis
* Occurs in body cells
Both
* Occurs in gametes cells
* Divides once
* Divides twice (meiosis 1 & II
* Creation of new cells
* Creates 2 cells
* Creates 4 cells
* DNA replicates once
* Are genetically identical
* Are NOT genetically identical
* Increases genetic diversity

51. This results in gametes with abnormal numbers of chromosomes:
Clicker Question #18
This results in gametes with abnormal numbers of chromosomes:
meiosis
mitosis
non-disjunction
crossing-over

52. This is an example of non-disjunction:
Clicker Question #19
This is an example of non-disjunction:
Color blindness
Down Syndrome
Cystic fibrosis
Sickle cell anemia

53. Answer: NO...They are using Binary Fission
Many Bacteria & protozoans do not need a partner to reproduce. Are they reproducing using mitosis?
Answer: NO...They are using Binary Fission
Binary Fission – Asexual form of reproduction used by some prokaryotes in which a cell divides into two genetically identical cells. (creates a new individual)
SIMILAR/LIKE “cloning” themselves
1 bacterium could become 1,000,000,000 (billion) in 10 hours!

54. What are the advantages & disadvantages to being asexual & sexual?
Asexual Reproduction
Advantages
Disadvantages
Can reproduce without a partner…
They don’t have to find a mate/partner.
No genetic variation…They are clones. Its putting all your eggs in one basket. If a something kills the parent, it WILL kill ALL the offspring too. Easily becomes extinct with little change to environment.
Able to reproduce quickly. The greater the number of offspring, the better the survival rate of the population.
Quick reproduction is also a disadvantage because too many individuals will be competing with each other for food & space

55. What are the advantages & disadvantages to being asexual & sexual?
Sexual Reproduction
Advantages
Disadvantages
Genetic diversity!
Has the ability to create endless recombination of genes (crossing-over) coming from 2 parents, all individuals are different in some way.
Must find a partner. Very difficult if the population is low and spread out.
Difficult to recover if the species is endangered.
The species is more able to adapt to environmental changes
Slow reproduction….takes time…
Slow population growth

56. Prokaryotes reproduce using:
Clicker Question #20
Prokaryotes reproduce using:
meiosis
mitosis
binary fission
binary fusion

57. Which of the following is an advantage of asexual reproduction
Clicker Question #21
Which of the following is an advantage of asexual reproduction
genetic diversity
the ability to reproduce quickly
the ability to adapt to new habitats
slow reproduction

58. Which of the following is an advantage of sexual reproduction
Clicker Question #22
Which of the following is an advantage of sexual reproduction
genetic diversity
the ability to reproduce quickly
the ability to reproduce many offspring
do not have to find a sexual partner

59. The End