1. Inquiry into Life Twelfth Edition
Lecture PowerPoint to accompany
Inquiry into Life Twelfth Edition
Sylvia S. Mader
Chapter 5
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 5.1 Cell Increase and Decrease
Cell division increase the number of somatic cells (body cells)

3. 5.1 Cell Increase and Decrease
Cell division increase the number of somatic cells (body cells)
Zygote Trillions of cells

4. 5.1 Cell Increase and Decrease
Cell division increase the number of somatic cells (body cells)
Mitosis: Division of the nucleus

5. 5.1 Cell Increase and Decrease
Cell division increase the number of somatic cells (body cells)
Mitosis: Division of the nucleus
Cytokinesis: Division of the cytoplasm

6. 5.1 Cell Increase and Decrease
Cell division increase the number of somatic cells (body cells)
Mitosis: Division of the nucleus
Cytokinesis: Division of the cytoplasm
Apoptosis: Programmed cell death

7. 5.1 Cell Increase and Decrease
The Cell Cycle
Orderly set of stages that occur between the time a cell divides and the time the resulting daughter cells divide

8. 5.1 Cell Increase and Decrease
The Cell Cycle
Interphase G1 S G2
Mitotic Stage
Mitosis and Cytokinesis

9. 5.1 Cell Increase and Decrease
The Cell Cycle
Interphase G1 S G2
Mitotic Stage
Mitosis and Cytokinesis

10. The Cell Cycle

11. 5.1 Cell Increase and Decrease
Control of the Cell Cycle
Internal and External Signals
Signaling proteins called cyclins increase and decrease as the cell cycle continues
Three Checkpoints G1 G2 M

12. The Cell Cycle

13. 5.1 Cell Increase and Decrease
Apoptosis
Cells undergo programmed cell death when they cannot complete mitosis or in response to external signals.

14. Apoptosis

15. 5.2 Maintaining the Chromosome Number

16. 5.2 Maintaining the Chromosome Number
Terms:
Chromatin: tangled mass of threadlike DNA in a non-dividing cell

17. 5.2 Maintaining the Chromosome Number
Terms:
Chromatin: tangled mass of threadlike DNA in a non-dividing cell
Chromosomes: condensed DNA molecules observed in dividing cells

18. 5.2 Maintaining the Chromosome Number
Terms:
Chromatin: tangled mass of threadlike DNA in a non-dividing cell
Chromosomes: condensed DNA molecules observed in dividing cells
Diploid (2n): Cells have two (a pair) of each type of chromosome

19. 5.2 Maintaining the Chromosome Number
Terms:
Chromatin: tangled mass of threadlike DNA in a non-dividing cell
Chromosomes: condensed DNA molecules observed in dividing cells
Diploid (2n): Cells have two (a pair) of each type of chromosome
Haploid (1n): Cells have half the diploid number of chromosomes

20. 5.2 Maintaining the Chromosome Number
Overview of Mitosis
Nuclear division in which chromosome number stays constant
DNA replication produces duplicated chromosomes
Each duplicated chromosome is composed of 2 sister chromatids held together by a centromere
Sister chromatids are genetically identical
During mitosis, the centromere divides and each chromatid becomes a daughter chromosome

21. Chromosomes and Chromatids

22. Mitosis Overview

23. 5.2 Maintaining the Chromosome Number
Mitosis in Detail - Animal Cells
Prophase-nuclear membrane disappears, centrosomes migrate, spindle fibers appear
Metaphase-chromosomes line up at metaphase plate, associated with spindle fibers
Anaphase-centromeres divide, sister chromatids migrate to opposite poles, cytokinesis begins
Telophase-nuclear membranes form, spindle disappears, cytokinesis occurs

24. Mitosis in Detail - Animal Cells

25. 5.2 Maintaining the Chromosome Number
How Plant Cells Divide
Occurs in meristematic tissues
Same phases as animal cells
Plant cells do not have centrioles or asters

26. Mitosis in Detail - Plant Cells

27. 5.2 Maintaining the Chromosome Number
Cytokinesis in Plant Cells
Flattened, small disk appears between daughter cells
Golgi apparatus produces vesicles which move to disk
Release molecules which build new cell walls
Vesicle membranes complete plasma membranes

28. Cytokinesis in Plant Cells

29. 5.2 Maintaining the Chromosome Number
Cytokinesis in Animal Cells
Cleavage furrow forms between daughter nuclei
Contractile ring contracts deepening the furrow
Continues until separation is complete

30. Cytokinesis in Animal Cells

31. 5.2 Maintaining the Chromosome Number
Cell Division in Prokaryotes: Binary Fission
Prokaryotes have a single chromosome
Chromosomal replication occurs before division
Cell begins to elongate to twice its length
Cell membrane grows inward until division is complete

32. Binary Fission

33. 5.3 Reducing the Chromosome Number

34. 5.3 Reducing the Chromosome Number
Meiosis
Occurs in the life cycle of sexually reproducing organisms
Reduces the chromosome number
Provides offspring with a different combination of traits from that of either parent

35. 5.3 Reducing the Chromosome Number
Overview of Meiosis
2 divisions, 4 daughter cells
Cells are diploid at beginning of meiosis
Pairs of chromosomes are called homologues

36. 5.3 Reducing the Chromosome Number
Overview of Meiosis
Meiosis I
Homologues line up side by side at equator-synapsis
When pairs separate, each daughter cell receives one member of the pair
Cells are now haploid

37. Meiosis

38. 5.3 Reducing the Chromosome Number
Overview of Meiosis
Meiosis II
No replication of DNA occurs in this division
Centromeres divide and sister chromatids migrate to opposite poles to become individual chromosomes
Each of the four daughter cells produced has the haploid chromosome number and each chromosome is composed of one chromatid

39. Meiosis

40. 5.3 Reducing the Chromosome Number
Overview of Meiosis
Fertilization
Fertilization restores the diploid number of chromosomes in a cell that will develop into a new individual.

41. 5.3 Reducing the Chromosome Number
Meiosis in Detail
Genetic Recombination Occurs in Two Ways
Crossing Over
Independent Assortment

42. Crossing Over

43. Independent Assortment

44. 5.3 Reducing the Chromosome Number
Phases of Meiosis I
Prophase I
Synapsis occurs, nuclear membrane breaks down
Homologues line up side by side and crossing over occurs
Metaphase I
Homologous pairs line up at metaphase plate such that maternal or paternal member may be oriented toward either pole

45. 5.3 Reducing the Chromosome Number
Phases of Meiosis I
Anaphase I
Homologous chromosomes (each still consisting of 2 chromatids) undergo independent assortment into daughter cells
Telophase I
Cytokinesis produces 2 daughter cells which are haploid

46. Phases of Meiosis I
Fig 5.12

47. 5.3 Reducing the Chromosome Number
Interkinesis - period of time between Meiosis I and Meiosis II
Phases of Meiosis II
Prophase II-
Cells have one member of each homologous pair
Metaphase II
Chromosomes line up at the metaphase plate

48. 5.3 Reducing the Chromosome Number
Phases of Meiosis II
Anaphase II
Centromeres divide and daughter chromosomes migrate
Telophase II
Nuclei form, cytokinesis

49. Phases of Meiosis II
Fig 5.13

50. 5.3 Reducing the Chromosome Number
Nondisjunction
The failure of paired chromosomes or chromatids to separate during cell division
Results in cells with an abnormal number of chromosomes
Trisomy 21 (Down syndrome) is an example

51. 5.3 Reducing the Chromosome Number
Genetic Recombination
Promotes genetic variability
Independent assortment of paired chromosomes during metaphase I
Crossing over in prophase I
Both assure that gametes will contain different combinations of chromosomes
When fertilization occurs, the resulting offspring will be genetically unique

52. Comparison of Meiosis to Mitosis
DNA replication occurs only once prior to either meiosis and mitosis
Meiosis requires two divisions, mitosis only one
Meiosis produces four daughter cells, mitosis produces two
Daughter cells from meiosis are haploid, those from mitosis are diploid
Daughter cells from meiosis are genetically variable, while those from mitosis are genetically identical

53. Comparison of Meiosis to Mitosis

54. 5.5 The Human Life Cycle Requires both mitosis and meiosis
Meiosis in the female is called oogenesis
Meiosis in the male is called spermatogenesis
At fertilization, the resulting zygote divides by mitosis for the processes of growth and development
Mitosis is used for repair throughout life

55. Life Cycle of Humans

56. 5.5 The Human Life Cycle Spermatogenesis
Begins at puberty and continues throughout life
Primary spermatocytes (2n) divide in meiosis I to form two secondary spermatocytes (1n)
Secondary spermatocytes divide in meiosis II to produce four sperm

57. 5.5 The Human Life Cycle Oogenesis Begins in the fetus
Primary oocytes are arrested in prophase I
At puberty, one primary oocyte continues the process of meiosis during each menstrual cycle
Primary oocyte (2n) divides in meiosis I to produce one secondary oocyte (1n) and one polar body
Division is unequal as secondary oocyte receives most of the cell contents and half the chromosomes

58. 5.5 The Human Life Cycle Oogenesis
If the secondary oocyte is fertilized, meiosis II will proceed.
Another unequal division will occur, the egg receiving most of the cytosplasm. A second polar body is also formed.
The unequal divisions allows the egg to have all the cellular “machinery” it needs for embryonic development

59. Spermatogenesis and Oogenesis in Mammals

60. 5.5 The Human Life Cycle Summary
Spermatogenesis and oogenesis both utilize meiosis
Spermatogenesis begins at puberty and continues throughout life
Spermatogenesis produces one sperm per primary spermatocyte
Results in production of many sperm
Oogenesis results in one oocyte and up to three polar bodies per primary oocyte
Divisions are unequal, ovum receives most cell contents
Oogenesis begins prior to birth, stops until puberty, then resumes in a cyclic pattern
Cyclic release of oocytes continues until menopause when the process stops