1. Mitosis and Meiosis
Cell Division

2. Why Do Cells Divide? For growth, repair, and reproduction

3. Mitosis Organisms grow by the addition of cells
In multicellular organisms some of these cells perform unique functions (different from other cells).

4. Differentiation-The process of a cell becoming specialized and thus different.
Totipotent cells can differentiate into specialized cells. A multicellular organism can be formed from one totipotent cell.

5. When do cells divide?
Most limiting factor in size is the size of the cell membrane.
Cells must obtain nutrients
as volume increases, cell surface area does not increase as greatly
larger cells require a larger surface area for survival

6. What kind of cells divide?
Differentiated or specialized cells like body cells such as skin and brain cells
Gametes or sex cells.
Totipotent cells like stem cells.

7. If a Swiss Army knife were totipotent…..
Hidden in one stem cell is the ability to become any other kind of cell…like a brain cell…or a blood cell….or a skin cell!

8. Totipotent

9. Totipotent
The ability to turn into all the mature cell types of the body (as well as embryonic components that are required for development but do not become tissues of the adult body such as the placenta). Plant cells are totipotent and any cell can form an entire plant. (Cuttings from a plant can grow into the entire plant etc.)

10. Plant vs. Animal Cells
Under normal conditions once an animal cell becomes specialized or differentiated, it no longer can form an entire organism, it can only form specialized kinds of cells.

11. Cell Division vs. Nuclear Division
Cytokinesis: The actual division of the cytoplasm. Following mitosis this produces two new cells.
Mitosis: The division of the nucleus of the cell into two new nuclei. Mitosis Animation

12. Terminology
Chromatin - thin fibrous form of DNA and histone proteins

13. Anatomy of a Chromosome
p -arm
Centromere - point where sister chromatids are joined together
P=short arm; upward
Q=long arm; downward
Telomere-tips of chromosome
centromere
q-arm
chromatids
telomere

14. Sister Chromatids
Sister Chromatids are two exact copies of a chromosome attached together by a structure called a centromere. Sister chromatids are created during the interphase portion of the cell cycle when each of the chromosomes synthesizes a copy of itself.

16. Cell cycle - sequence of phases in the life cycle of the cell
How Do Cells Divide?
Cell cycle - sequence of phases in the life cycle of the cell

17. Cell cycle has two parts:
Getting ready to split
Cell cycle has two parts:
growth and preparation (interphase)
cell division
mitosis (nuclear division)
cytokinesis (cytoplasm division)

18. Interphase
Occurs between divisions
Longest part of cycle
3 stages

20. Interphase
G1 or Gap 1
The cell just finished dividing so in Gap 1 the cell is recovering from mitosis

21. Interphase S or Synthesis stage
DNA replicates before division an identical copy is the very first mission.

22. Interphase G 2 or Gap 2 This is preparation for mitosis
Organelles are replicated.
More growth occurs.

24. MITOSIS
Mitosis begins after G 2 and ends before G 1

25. Prophase Chromosome condense Microtubules form
The nuclear envelope breaks down

26. Metaphase
Chromosomes are pulled to center of cell
Line up along “metaphase plate”

28. Anaphase
Centromeres divide
Spindle fibers pull one set of chromosomes to each pole
Precise alignment is critical to division

30. Telophase Nuclear envelope form around chromosomes Chromosomes uncoil
Cytokinesis
animals - pinching of plasma membrane
plants- elongates and the cell plate forms( future cell wall and cell membrane)

31. Meiosis

32. What is Meiosis?
A division of the nucleus that reduces chromosome number by half.
Important in sexual reproduction
Involves combining the genetic information of one parent with that of the the other parent to produce a genetically distinct individual

33. Terminology
Diploid - two sets of chromosomes (2n), in humans 23 pairs or 46 total
Haploid - one set of chromosomes (n) - gametes or sex cells, in humans 23 chromosomes

34. Chromosome Pairing Homologous pair
each chromosome in pair are identical to the other ( carry genes for same trait)
only one pair differs - sex chromosomes X or Y

35. Phases of Meiosis A diploid cell replicates its chromosomes
Two stages of meiosis
Meiosis I and Meiosis II
Only 1 replication

37. Important vocabulary
Synapsis - pairing of homologous chromosomes forming a tetrad.
Crossing over - chromatids of tetrad exchange parts.

38. Meiosis I

39. Prophase I Chromosomes condense
Homologous chromosomes pair w/ each other
Each pair contains four sister chromatids - tetrad

40. Metaphase I
Tetrads or homologous chromosomes move to center of cell

41. Anaphase I
Homologous chromosomes pulled to opposite poles

42. Telophase I
Daughter nuclei formed
These are haploid (1n)

43. Meiosis II Daughter cells undergo a second division; much like mitosis
NO ADDITIONAL REPLICATION OCCURS

44. Prophase II
Spindle fibers form again

45. Metaphase II
Sister chromatids move to the center

46. Anaphase II Centromeres split
Individual chromosomes are pulled to poles

47. Telophase II & Cytokinesis
Four haploid daughter cells results from one original diploid cell

48. Review Mitosis & Meiosis
Both are forms of nuclear division
Both involve replication
Both involve disappearance of the nucleus, and nucleolus, nuclear membrane
Both involve formation of spindle fibers

49. DIFFERENCES
Meiosis produces daughter cells that have 1/2 the number of chromosomes as the parent. Go from 2n to 1n.
Daughter cells produced by meiosis are not genetically identical to one another.
In meiosis cell division takes place twice but replication occurs only once.

50. Value of Variation
Variation - differences between members of a population.
Meiosis results in random separation of chromosomes in gametes.
Causes diverse populations that over time can be stronger for survival.