1. Cell Division
Mitosis & Meiosis

2. Learning Target I can describe the basic process of mitosis.
(Quality Core Standard B.1.j)

3. Why is it important to me?
Cell Division
What is it?
Why do Cells do it?
Why is it important to me?

4. Takes place in Regular Body Cells
Cell Division
Also known as Mitosis
Takes place in Regular Body Cells
Keeps Cells Living and Growing

5. Why Do Cells Divide? Two main reasons:
1. The larger a cell becomes, the more demands the cell places on it's DNA.

6. Food goes in
2. The bigger the cell gets the harder it becomes to move food and waste across the membrane
Waste goes out

7. Protein Pumps
This happens because the surface area and volume ratio does not stay the same as the cell size increases.

8. The cell's ability to either get substances from the outside or eliminate waste from the inside is related to the surface area of the cell membrane. (outside)

9. How much food and other material is required, and how much waste the cell produces and has to get rid of, is related to the volume of the cell. (inside)

10. As a cell gets bigger there comes a time when its surface area is not large enough to meet the demands of the cell's volume and the cell stops growing.

11. So, once cells reach a certain size they must divide in order to continue to function – or they will no longer be able to take in nutrients and eliminate waste.

12. Why Is Cell Division Important?
1. All Living Things are made of Cells

13. 2. The Cell is the basic unit of Structure and Function in Living Things.

14. 3. All Cells come from pre existing Cells
These three statements are part of what?

15. You are a living organism, made of cells.
In order to keep living, your cells must stay alive.
In order for cells to keep living, they must divide and multiply

16. Phases of Mitosis

17. The Basic Phases of a Cell’s Life Cycle:
Interphase G1 S G2
Mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

18. The longest stage of a Cell’s life
Interphase
The longest stage of a Cell’s life
The time spent between divisions
Produces all materials required for growth
Preparation for division

19. Interphase: G1
Growth Phase
Cells do most of their growing and synthesize new proteins and organelles.

20. Interphase: S Phase
(Synthesis Phase)
Chromosomes are duplicated and DNA is synthesized
If the cell gets to this phase, division will be completed.

21. Mitosis Interphase: G2 Shortest phase
Many organelles and other molecules are made
Next step –
Mitosis

22. Mitosis: Cell Division
The last part of the Cell Cycle is called Mitosis and has 4 phases during which the cell divides into 2 cells

23. The Cell begins the division process
Prophase
The Cell begins the division process
1.The nucleolus disappears
2.The nuclear membrane breaks apart

24. 3. The chromosomes
become visible
4. The spindle
apparatus forms
and attaches to
the centromeres
of the
chromosomes

25. The Second Phase of Mitosis
Metaphase
The Second Phase of Mitosis
The Nuclear Membrane is completely gone
2. The duplicated chromosomes line up along the cell's equator.

27. Anaphase The third phase of Mitosis Daughter chromosomes separate
They are pushed and pulled toward opposite poles of the cell by the spindle fibers

28. Spindle Fibers

29. Telophase The nuclear membrane and nucleoli and nucleus reform.
Cytokinesis is nearly complete,

30. The Cell Plate begins to form
The Cell prepares for final division

31. Cytokinesis – The final stage of the cell cycle
The cytoplasm, organelles, and nuclear material are evenly split and two new cells are formed.
Cell Plate

32. The two new cells – each exactly like the other – are called Daughter Cells

33. Learning Target I can describe the basic process of mitosis
(Quality Core Standard B.1.j)

34. Meiosis
Why We Are Who We Are

35. Learning Target I can describe the basic process of meiosis.
(Quality Core Standard C.1.f)

36. Meiosis
Process of reduction division. Number of chromosomes per cell is cut in half.
Occurs when two organisms join gametes to form the first cell of a new individual
Gametes are sperm and egg; or pollen and ovule
All of our cells are diploid meaning we have two copies of each chromosome

37. Meiosis
One chromosome comes from the male parent; the other from the female: homologous
Our sex cells: sperm and egg are haploid meaning these special cells only have half the chromosomal complement
Involves two divisions of the nucleus called Meiosis I and Meiosis II

38. Prophase I Chromosomes condense Nuclear envelope breaks down
Homologous chromosomes
pair all along their length forming tetrads (4 chromatids)
Crossing over occurs when
parts of one chromosome are
broken and exchanged with
the same parts on its
corresponding chromosome

39. Metaphase I Pairs of homologous chromosomes
are moved by spindle fibers to the
equator of the cell
Homologous chromosomes,
each made of two chromatids
stay together

40. Anaphase I Homologous chromosomes separate
Chromosomes of each pair are
pulled to opposite poles by
spindle fibers
Chromatids do not separate at
the centromeres—each is still
made of two chromatids

41. Telophase I & Cytokinesis
Individual chromosomes gather
at each pole
Cytokinesis occurs forming
two new cells
Both cells contain one chromosome
from each pair of homologous
chromosomes
The chromosomes do not replicate
between Meiosis I and II

42. Prophase II
New spindle forms around chromosomes

43. Metaphase II Chromosomes line up at equator
Attached at centromeres to spindle fibers

44. Anaphase II Centromeres divide
Chromatids (chromosomes) move to opposite poles

45. Telophase II Nuclear envelope forms around each set of chromosomes
Spindle breaks down
Cytokinesis occurs
Four haploid cells are created, each carrying one set of chromosomes

46. Meiosis Contributes to genetic variation by way of three mechanisms:
Independent assortment
Crossing over
Random fertilization

47. Independent Assortment
Each gamete receives one chromosome from each of the 23 pairs of homologous chromosomes
The random distribution of homologous chromosomes is independent assortment
Each of the 23 pairs independently separates so that 223 (about 8 million gametes are possible from just one cell)

48. Crossing over
An exchange of DNA segments between two homologous chromosomes
In Prophase I, the chromosomes have made a tetrad with each pair of chromatids joined at centromeres
Crossing over occurs at chiasma
When recombined offspring may have one trait from each parent: dad’s eyes and mom’s hair

49. Crossing over

50. Random Fertilization
The zygote that forms a new individual is the result of random joining of gametes
Each new sperm or new egg is vastly different from one another due to the different combination

51. Meiosis in Males

52. Meiosis in Males Process is called spermatogenesis Occurs in testes
Can occur throughout males life once hits puberty
At end of meiosis, four complete sperm cells are made

53. Meiosis in Females

54. Meiosis in Females Called oogenesis Occurs in ovaries
Cytokinesis causes uneven splitting of cytoplasm in Meiosis I
One cell gets most of cytoplasm and is much larger; small one is called polar body
Meiosis II; same process again. One large cell is made; three small polar bodies die
Large ovum is made that has enough nutrients for zygote during its initial formation

55. Learning Target I can describe the basic process of meiosis.
(Quality Core Standard C.1.f)