1. Cell Division
Chapter 5

2. Why does a cell divide?
As a cell absorbs nutrients and gets larger, the volume of the cell increases faster than the surface area.
-Therefore, the demands of the cell (the volume) exceed the ability of the cell to bring in nutrients and export wastes. Solution?
Divide into two smaller cells

3. Cell Increase and Decrease
Cell division:
Mitosis (division of nucleus or karyokinesis)
Cytokinesis (division of cytoplasm)
Apoptosis (cell death) decreases the number of cells.
Both cell increase and apoptosis occur during normal development and growth.

4. Cell Division, Cell Death
Functions of Cell Division
Mitosis
Increase number of somatic cells
Wound healing
Asexual reproduction
Meiosis
Production of gametes (germ cells, sperm and eggs)
Apoptosis—Programmed cell death
Amoeba

5. Asexual reproduction 2
Hydra

6. The cell cycle

7. Interphase—3 Stages G1 stage – S stage – G2 stage – cell growth
cell doubles its organelles
accumulates materials for DNA synthesis
S stage –
DNA synthesis occurs
DNA replication results in duplicated chromosomes
G2 stage –
cell synthesizes proteins needed for cell division

8. Chromosomes
Chromosome – Condensed chromatin

9. Homologous Chromosomes
Same size
Same genes in the same order
Chromosome pairs, one from mom, one from dad

10. a. Diploid number (2n) - total number of chromosomes in a cell (somatic cells)
b. Haploid number (n) - only one homologue of each chromosome is present (gametes)

11. The Big Picture

13. The Cell Cycle
Interphase (90% of cycle) • G1 phase~ growth • S phase~ synthesis of DNA • G2 phase~ preparation for cell division
Mitotic phase • Mitosis~ nuclear division • Cytokinesis~ cytoplasm division

14. The Mitotic Stage
Following interphase is the M stage, including mitosis and cytokinesis.
During mitosis, sister chromatids of each chromosome separate.
The cell cycle ends when cytokinesis, the cleaving of the cytoplasm, is complete.

15. Figure 5.30 The DNA double helix and its replication

16. In mitosis each chromosome is replicated and then divides

17. Duplicated Chromosome
Sister chromatids attached at centromere
Sister chromatids separate during cell division

18. PLOIDY
Ploidy - number of copies of each chromosome - also number of genomes
Haploid (N)= one set of unpaired chromosomes
Diploid (2N or 2n)= one set of paired chromosomes
Triploid = three copies of each chromosome
Tetraploid = four copies of each chromosome
Hexaploid = six copies of each chromosome
Etc, etc, etc

19. Chloroplasts have their own DNA, separate from
plant nuclear DNA, derived from their cyanobacterial origin

20. Most eukaryotes also have a mitochondrial genome, derived from a eubacterial endosymbiont ancestor
Human mtDNA 37 genes, 16 kilobasepairs

21. Apoptosis
Apoptosis - programmed cell death.
Function?

22. Mitosis Overview
1 diploid (2N) cell>>>>2 diploid (2N)cells
Genetically identical daughter cells
Function---Maintain the somatic cell chromosome number

23. Mitosis Overview

25. Chromosome Distribution

26. Spindle and Fibers Spindle made of? Centrosomes (MTOC)—function?
microtubules that disassemble and assemble.
Centrosomes (MTOC)—function?
Types of Fibers
Polar Spindle Fibers
Centomeric (kinetochore) fibers
Asters

27. Phases of Mitosis Prophase Metaphase Anaphase Telophase
Pretty Men Are Tough
Overview

28. As cell enters mitosis from interphase it has 2 complete sets of chromosomes because of replication in the S phase. Each set must be re-arranged and distributed into the 2 new daughter nuclei. This is mitosis.

29. Late Interphase

30. Early Prophase

31. Late Prophase

32. Metaphase

33. Anaphase

34. Telophase
Review

35. Results of Mitosis Two daughter nuclei
Each with same chromosome number as parent cell
Genetically identical to each other and the parent cell

36. CYTOKINESIS – Cytoplasm splits into 2 cells.
-Animal cells: Cleavage furrow forms from outside in. -
Plant cells: Division plate forms from inside out.

37. Cytokinesis in Animal Cells

38. Cytokinesis in plant cells

39. REVIEW OF MITOSIS Remember: Mitosis Is Part Of The Cell Cycle!!
Parent Cell
Remember:
Mitosis Is Part
Of The Cell Cycle!!
DNA Synthesis (“S” Phase)
Mitosis & Cytokinesis
Two daughter cells
Parent cell and daughter cells contain the same complement of chromosomes.

40. Cell Division in Prokaryotes
Binary fission---process of asexual reproduction in prokaryotes.
Two daughter cells
Identical to the original parent cell and each other
All contain a single chromosome.

41. The Big Picture

42. Overview of Meiosis
1 diploid (2N) cell>>>>4 haploid (1N) cells
Genetically unique daughter cells
Function---reduce the chromosome number by ½
The main source of genetic diversity in sexually reproducing organisms

43. MEIOSIS Two Parts: Meiosis I: Meiosis II:
Separation of homologous pairs
Ploidy Level?
Meiosis II:
Separation of sister chromatids

44. COMPARISON-- MITOSIS and MEIOSIS
Occurs in somatic (body) cells
Growth, development, replacement & repair
Produces 2 daughter cells
Clones of parent and each other
Daughter cells are diploid (2N)
Meiosis:
Occurs in germ cells (immature reproductive cells)
Production of gametes (sex cells)
Produce 4 daughter cells
Distinct from parent and each other
Daughter cells are haploid (1N)

45. Genetic Recombination
Meiosis increases genetic diversity. Two points of genetic recombination.
Crossing-over of nonsister chromatids—Prophase 1
Independent assortment of homologous chromosomes during Metaphase 1

46. Synapsis and crossing-over.
Defs

47. More Terminology Crossing Over Synapsis Tetrad
Segments of paternal/maternal chromatids exchange during Meiosis I
Synapsis
Process of homologs coming together physically during Meiosis I
Tetrad
Consists of 4 sister chromatids from 2 homologous chromosomes

48. Independent assortment.

49. Meiosis in Detail Phases Interkinesis. Replication of DNA?? Prophase
Metaphase
Anaphase
telophase
Interkinesis.
Replication of DNA??

50. Meiosis I in an animal cell

52. Meiosis II

54. Sources of Genetic Variation
Three sources of genetic recombination:
Independent alignment – metaphase I
Crossing-over---prophase I
Fertilization

55. SUMMARY-- MITOSIS and MEIOSIS
Occurs in somatic (body) cells
Growth, development, replacement & repair
Produces 2 daughter cells
Clones of parent and each other
Daughter cells are diploid (2N)
Meiosis:
Occurs in germ cells (immature reproductive cells)
Production of gametes (sex cells)
Produce 4 daughter cells
Distinct from parent and each other
Daughter cells are haploid (1N)
comparison

56. Meiosis compared to mitosis

57. Life cycle of humans

58. Spermatogenesis

59. Oogenesis

60. FERTILIZATION RESTORES FULL SET OF CHROMOSOMES
Female gamete
Male gamete
fertilization
Diploid zygote contains homologous pairs of chromosomes

61. Sources of Genetic Variation
Three sources of genetic recombination:
Independent assortment – metaphase I
Crossing-over---prophase I
Fertilization

62. MEIOSIS & GENETIC VARIATION
Independent Assortment
Diploid organisms can produce 2n diff. gametes
Ea. homologous pair can orient in two different ways
Humans: 223 = 8,388,608
(est. 8.4 million)
Each homologous pair can orient in either of two ways

63. HYPOTHETICAL EXAMPLE OF INDEPENDENT ASSORTMENT
Eye color
Hair color
Gene for brown eyes
Gene for blue eyes r
Gene for black hair
Gene for red hair

64. INDEPENDENT ASSORTMENT
During meiosis I, tetrads can line up 2n different ways. OR
Meiosis I & II
Brown eyes Black hair
Blue eyes Red hair
Blue eyes Black hair
Brown eyes Red hair

65. MEIOSIS & GENETIC VARIATION
Crossing Over:
Physical exchange of sections of chromosomes
Results in shuffling of genome
New combo of genes on chromosomes (recombination)
A single crossover in each homologous pair = 5.0 x different zygotes possible (4951,760,200,000,000,000,000,000,000)!

66. MEIOSIS & GENETIC VARIATION
Random Fertilization:
Each human can produce an nearly 8.4 million different kinds of gametes
Crossing over not taken into account!!!
Sex yields:
8.4 mill x 8.4 mill = 70.6 x genetically distinct offspring can be produced

67. SUMMARY-- MITOSIS and MEIOSIS
Occurs in somatic (body) cells
Growth, development, replacement & repair
Produces 2 daughter cells
Clones of parent and each other
Daughter cells are diploid (2N)
Meiosis:
Occurs in germ cells (immature reproductive cells)
Production of gametes (sex cells)
Produce 4 daughter cells
Distinct from parent and each other
Daughter cells are haploid (1N)
comparison