1. Cellular Division

2. Purpose of Cell Division:
In prokaryotes: Asexual reproduction
In eukaryotes: Make new cells for growth and replace damaged or old cells

3. Keeping Cells Identical
The instructions for cells are in the DNA.
Each new cell must get a complete set of the DNA.

4. Two new, identical DNA strands
DNA Replication
DNA must be copied or replicated before cell division
Each daughter cell will receive an identical copy of the DNA
Original DNA strand
Two new, identical DNA strands

5. Identical Daughter Cells
Two identical daughter cells
Parent Cell

6. Chromosomes

7. Prokaryotic Chromosome
In prokaryotes (bacteria),
DNA is one, circular piece of DNA
also have plasmids – small, extra pieces of DNA.

8. Cell Division in Prokaryotes

9. Cell Division in Prokaryotes
Prokaryotes divide by binary fission
First, the single piece of DNA makes a copy of itself
The cell splits
A cell wall forms between the new cells
Parent cell
Chromosome relicates
Cell splits
2 identical daughter cells

10. Prokaryotic Cell Undergoing Binary Fission

11. Eukaryotic Cells have chromosomes
Most eukaryotes have
chromosomes in
their body cells
Human body cells
have 46
chromosomes
(23 pairs)

12. Eukaryotic Chromosomes
Each chromosome is composed of a single, tightly coiled DNA molecule
Chromosomes can’t be seen when cells aren’t dividing and are called chromatin

13. Compacting DNA into Chromosomes
Before division, DNA tightly coils around histone proteins

14. Chromosomes in Dividing Cells
Before division, chromosomes replicate.
Duplicated chromosomes are called chromatids & are held together by the centromere
Called Sister Chromatids

15. Karyotype
A picture of the chromosomes from a human cell arranged in pairs by size
First 22 pairs are called autosomes
Last pair are the sex chromosomes
XX female or XY male

16. The Y Chromosome Decides
Boy or Girl?
The Y Chromosome Decides
Y - Chromosome
X - Chromosome

17. Cell Reproduction in Eukaryotes

18. The events in eukaryotic cell division are described as the Cell Cycle

19. Phases of the Cell Cycle
Phase 1 – Interphase
3 parts:
G1 - primary growth phase
S – synthesis; DNA replicated
G2 - secondary growth phase
Phase 2 – mitosis
Phase 3 - cytokinesis

20. Interphase - G1 Stage
Cells grow and mature by making more cytoplasm & organelles

21. Two identical copies of DNA
Interphase – S Stage
Synthesis stage
DNA is copied or replicated
Two identical copies of DNA
Original DNA

22. Interphase – G2 Stage 2nd Growth Stage
All the cell structures that are needed for division are made (e.g. centrioles)

23. Mitosis

24. Mitosis Doesn’t occur in some cells such as brain cells
Has four stages

25. Four Mitotic Stages
Prophase
Metaphase
Anaphase
Telophase

26. Early Prophase
Chromatin in nucleus condenses (gets thick) to form visible chromosomes
Mitotic spindle forms
Cytoplasm
Nucleolus
Nuclear Membrane
Chromosomes

27. Late Prophase Nuclear membrane & nucleolus are broken down
Spindle fibers attach to the centromere of each chromosome

28. Nucleus & Nucleolus have disintegrated
Late Prophase
Chromosomes
Nucleus & Nucleolus have disintegrated

29. Metaphase
Chromosomes move to the center of the cell and line up at the equator
Equator of Cell
Pole of the Cell

30. Metaphase Asters at the poles Spindle Fibers
Chromosomes lined at the Equator

31. Chromosomes at Equator
Metaphase
Aster
Chromosomes at Equator

32. Anaphase
Sister chromatids are pulled apart to opposite poles of the cell

33. Sister Chromatids being separated
Anaphase
Sister Chromatids being separated

34. Telophase Sister chromatids reach opposite poles
Nuclear envelope forms around each set of sister chromatids
Nucleolus reappears
CYTOKINESIS occurs

35. Cytokinesis Means division of the cytoplasm
Division of cell into two, identical halves called daughter cells
In plant cells, cell plate forms at the equator to divide cell
In animal cells, cleavage furrow forms to split cell

36. Cleavage furrow in animal cell Cell plate in plant cell
Cytokinesis
Cleavage furrow in animal cell
Cell plate in plant cell

37. Mitotic Stages

38. Daughter Cells of Mitosis
Have the same number of chromosomes as the parent cell
Identical to each other, but smaller than parent cell
Must grow in size to become mature cells (G1 of Interphase)

39. Review of Mitosis

40. Review: Interphase Name this? Prophase Telophase Name this? Metaphase
Anaphase

41. Eukaryotic Cell Division
Cells are diploid (2n)
Cytokinesis
Anaphase
Prophase
Metaphase
Telophase

42. Name each stage as you see it occur?
Mitosis Animation
Name each stage as you see it occur?

43. Mitosis in Onion Root Tips
Do you see any stages of mitosis?

44. Draw & Learn these Stages

45. Draw & Learn these Stages

46. Test Yourself over Mitosis

47. Mitosis Quiz

48. Mitosis Quiz

49. Name the Stages of Mitosis:
Early prophase
Early Anaphase
Metaphase
Interphase
Early Telophase,
Begin cytokinesis
Late Prophase
Late telophase,
Advanced cytokinesis
Mid-Prophase
Late Anaphase

50. Early, Middle, & Late Prophase Telophase & Cytokinesis
Identify the Stages ?
Early, Middle, & Late Prophase ? ? ?
Metaphase
Anaphase
Late Prophase ? ? ?
Telophase & Cytokinesis
Late Anaphase
Telophase

51. Locate the Four Mitotic Stages in Plants
Anaphase
Telophase
Metaphase
Prophase

52. Uncontrolled Mitosis Cancer cells
If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors
Oncogenes are genes that increase the chance that a normal cell develops into a tumor cell
Cancer cells

53. Meiosis Formation of Gametes (Eggs & Sperm)

54. Facts About Meiosis Two meiotic divisions ---
Meiosis I and Meiosis II
Called Reduction division
Original cell is diploid (2n)
Four daughter cells produced that are haploid (1n)

55. Facts About Meiosis
Daughter cells contain half the number of chromosomes as the original cell
Produces gametes (eggs & sperm)
Occurs in the testes in males (Spermatogenesis)
Occurs in the ovaries in females (Oogenesis)

56. After division - 23 chromosomes (1n)
Start with 46 double stranded chromosomes (2n)
After division - 23 chromosomes (1n)

57. Why Do we Need Meiosis?
Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote

58. Fertilization – “Putting it all together”

59. Replication of Chromosomes
Replication is the process of duplicating a chromosome
Occurs prior to division
Replicated copies are called sister chromatids
Held together at centromere
Occurs in Interphase
Replication is the process of duplicating chromosome. The new copy of a chromosome is formed by DNA synthesis during S-phase. The chromosome copies are called sister chromatids. Sister chromatids are held together at the centromere.

60. Meiosis Forms Haploid Gametes
Meiosis must reduce the chromosome number by half
Fertilization then restores the 2n number
from mom
from dad
child
too
much!
meiosis reduces
genetic content
The right number!

61. Each diploid cell contains a pair of matching chromosomes – one from mom and one from dad.
These are called HOMOLOGOUS CHROMOSOMES or HOMOLOGS.

62. Meiosis: Two Part Cell Division
Sister
chromatids
separate
Meiosis I
Meiosis II
Homologs
separate
Diploid
Haploid
Haploid

63. Prophase I
Early prophase
Homologs pair.
Crossing over occurs.

64. Homologous chromosomes (each with sister chromatids)
Homologs form Tetrads
Homologous chromosomes (each with sister chromatids)  
Join to form a TETRAD
Called Synapsis

65. Crossing-Over Homologous chromosomes in a tetrad cross over each other
Pieces of chromosomes or genes are exchanged
Produces Genetic recombination in the offspring

66. Crossing-Over
Crossing-over multiplies the already huge number of different gamete types

67. Results of Meiosis Gametes (egg & sperm) form
Four haploid cells with one copy of each chromosome

68. Oogenesis or Spermatogenesis
Gametogenesis
Oogenesis or Spermatogenesis

69. Spermatogenesis Meiosis in the testes
Two divisions produce 4 spermatids
Spermatids mature into sperm
Men produce about 250,000,000 sperm per day

70. Spermatogenesis in the Testes
Spermatid

71. Oogenesis Meiosis in the ovaries
Two divisions produce 3 polar bodies that die and 1 egg
Polar bodies die because of unequal division of cytoplasm
Immature egg called oocyte
Starting at puberty, one oocyte matures into an ovum (egg) every 28 days

72. Oogenesis in the Ovaries

73. Comparing Mitosis and Meiosis

74. Comparison of Divisions
Mitosis
Meiosis
Number of divisions 1 2
Number of daughter cells 4
Genetically identical?
Yes No
Chromosome #
Same as parent
Half of parent
Where
Somatic cells
Germ cells
When
Throughout life
At sexual maturity
Role
Growth and repair
Sexual reproduction