1. Chapter 8: Cell Reproduction Original slide set from: www.laney.edu/wp/laura_coronado/files/2011/08/SVChap- 8.ppt

2. WHAT CELL REPRODUCTION ACCOMPLISHES  Reproduction: May result in the birth of new organisms More commonly involves the production of new cells

3. Cell Division  Cell division plays important roles in the lives of organisms. Replaces damaged or lost cells Permits growth Allows for reproduction

4. Cell Replacement Growth via Cell Division FUNCTIONS OF CELL DIVISION Human kidney cell Early human embryo LM Colorized TEM Figure 8.1a

5. Asexual Reproduction Single-celled organisms reproduce by simple cell division There is no fertilization of an egg by a sperm The parent and its offspring have identical genes.

6. Asexual Reproduction Binary Fission Prokaryotic cells divide through a simple form of division called Binary Fission Prokaryotic cells divide through a simple form of division called Binary Fission 3 step process 3 step process Single “naked” strand splits and forms a duplicate of itself. Single “naked” strand splits and forms a duplicate of itself. The two copies move to opposite sides of the cell The two copies move to opposite sides of the cell Cell “pinches” into two new and identical cells called "daughter cells". (Cell wall then forms if applicable) Cell “pinches” into two new and identical cells called "daughter cells". (Cell wall then forms if applicable)

7. Asexual Reproduction Mitosis is the type of cell division responsible for:  Asexual reproduction  Growth and maintenance of multicellular organisms  Some multicellular organisms, such as sea stars, can grow new individuals from fragmented pieces.  Growing a new plant from a clipping

8. Asexual Reproduction FUNCTIONS OF CELL DIVISION Sea stars LM Amoeba African Violet Figure 8.1b

9. Sexual Reproduction  Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis.  Thus, sexually reproducing organisms use: Meiosis for reproduction Mitosis for growth and maintenance

10. Chromosomes LM Figure 8.3

11. Chromosomes  Chromosomes: Are made of chromatin, a combination of DNA and protein molecules Are not visible in a cell until cell division occurs –Before a parent cell splits into two, it duplicates its chromosomes

12. Number of chromosomes in body cells Indian muntjac deer Species Opossum Koala Human Mouse Giraffe Buffalo Dog Red viscacha rat Duck-billed platypus 102 78 60 54 46 40 30 22 16 6 Figure 8.2

13. Eukaryotic Cell Genetic Information  Most genes on chromosomes in cell nucleus  A few genes found in mitochondrial and chloroplast DNA  Each chromosome: one very long DNA molecule, typically with thousands of genes.  Histones are proteins used to package DNA.  Nucleosomes consist of DNA wound around histone molecules.

14. Duplicated chromosomes (sister chromatids) TEM Tight helical fiber Looped domains TEM Centromere Nucleosome “Beads on a string” Histones DNA double helix Figure 8.4 Laura Coronado Bio 10 Chapter 8

15. Duplicated chromosome Chromosome (one long piece of DNA) Centromere Sister chromatids Figure 8.UN2 Laura Coronado Bio 10 Chapter 8

16. Chromosomes  Before a cell divides, it duplicates all of its chromosomes, resulting in two copies called sister chromatids.  Sister chromatids are joined together at a narrow “waist” called the centromere.  When the cell divides, the sister chromatids separate from each other.  Once separated, each chromatid is: Considered a full-fledged chromosome Identical to the original chromosome

17. Chromosome duplication Sister chromatids Chromosome distribution to daughter cells Figure 8.5 Laura Coronado Bio 10 Chapter 8

18. The Cell Cycle  A cell cycle is the orderly sequence of events that extend from the time a cell is first formed from a dividing parent cell to its own division into two cells.  The cell cycle consists of two distinct phases: Interphase The mitotic phase

19. Cytokinesis (division of cytoplasm) Mitosis (division of nucleus) Mitotic (M) phase: cell division (10% of time) Interphase: metabolism and growth (90% of time) S phase (DNA synthesis; chromosome duplication) G1G1 G2G2 Figure 8.6 Laura Coronado Bio 10 Chapter 8

20. Interphase

21.  Most of a cell cycle is spent in interphase.  During interphase, a cell: Performs its normal functions Doubles everything in its cytoplasm Grows in size Laura Coronado Bio 10 Chapter 8

22. Interphase  3 Stages G1 (Gap 1) Phase - Cell performs its normal function (cells which do not divide stay in this stage for their entire life span)G1 (Gap 1) Phase - Cell performs its normal function (cells which do not divide stay in this stage for their entire life span) -cells grow and mature-cells grow and mature S (Synthesis) Phase - Here the cell actively duplicates its DNA in preparation for divisionS (Synthesis) Phase - Here the cell actively duplicates its DNA in preparation for division G2 (Gap 2) Phase - Amount of cytoplasm (including organelles) increases in preparation for division.G2 (Gap 2) Phase - Amount of cytoplasm (including organelles) increases in preparation for division. Another possibilityAnother possibility §G0 Phase cells do not prepare for cell division Generally straight from G1 phaseGenerally straight from G1 phase Example: fully developed cells in Central Nervous System never divide againExample: fully developed cells in Central Nervous System never divide again

23. Mitosis

24.  The mitotic (M) phase includes two overlapping processes: Mitosis, in which the nucleus and its contents divide evenly into two daughter nuclei Cytokinesis, in which the cytoplasm is divided in two

25. Mitosis and Cytokinesis  Mitosis consists of four distinct phases: (A) Prophase (B) Metaphase (C) Anaphase (D) Telophase  Cytokinesis typically: Occurs during telophase Divides the cytoplasm Is different in plant and animal cells

26. Nuclear envelope LM Plasma membrane Chromosome, consisting of two sister chromatids Spindle microtubules Fragments of nuclear envelope Centrosome Centromere Early mitotic spindle Centrosomes (with centriole pairs) Chromatin PROPHASEINTERPHASE Figure 8.7.a

27. Prophase Chromosomes condense Nuclear membrane breaks down Centrioles migrate to opposite poles (in animal cells) Microtubules attach to chromosomes and centrioles

28. Prophase

29. ANAPHASE METAPHASE TELOPHASE AND CYTOKINESIS Spindle Daughter chromosomes Cleavage furrow Nuclear envelope forming Figure 8.7b

30. Metaphase Chromosomes line up along the center of the cell

31. Metaphase

32. Anaphase Microtubules shorten Chromatids separate a pull to opposite sides

33. Anaphase

34. Telophase Nuclear membrane forms around each set of chromosomes Chromosomes unwind

35. Cytokinesis Cytoplasm split in two Cell membrane separates the two daughter cells

36. Telophase and Cytokinesis

37. Animal cell mitosis

38. Cleavage furrow SEM Cleavage furrow Contracting ring of microfilaments Daughter cells Figure 8.8a

39. Plant Cell Mitosis Plant cell mitosis is similar to animal cell mitosis BUT cytokinesis is different In plant, fungi and algae cell, a cell plate forms in the middle of the cell to divide the two cells.

40. Daughter cells New cell wall Vesicles containing cell wall material Cell plate Cell wall Wall of parent cell Cell plate forming Daughter nucleus LM Figure 8.8b

41. Result of Mitosis 2 daughter cells that are identical to each other and identical to the parent cell

42. Cancer Cells: Growing Out of Control  Normal plant and animal cells have a cell cycle control system that consists of specialized proteins, which send “stop” and “go-ahead” signals at certain key points during the cell cycle.

43. What Is Cancer?  Cancer is a disease of the cell cycle.  Cancer cells do not respond normally to the cell cycle control system.  Cancer cells can form tumors, abnormally growing masses of body cells.  The spread of cancer cells beyond their original site of origin is metastasis.  Malignant tumors can: Spread to other parts of the body Interrupt normal body functions

44. A tumor grows from a single cancer cell. Cancer cells invade neighboring tissue. Metastasis: Cancer cells spread through lymph and blood vessels to other parts of the body. Glandular tissue Blood vessel Tumor Lymph vessels Figure 8.9

45. Cancer Treatment  Cancer treatment can involve: Radiation therapy, which damages DNA and disrupts cell division Chemotherapy, which uses drugs that disrupt cell division

46. Cancer Prevention and Survival  Certain behaviors can decrease the risk of cancer: Not smoking Exercising adequately Avoiding exposure to the sun Eating a high-fiber, low-fat diet Performing self-exams Regularly visiting a doctor to identify tumors early

47. Meiosis

48. Homologous Chromosomes  Different individuals of a single species have the same number and types of chromosomes.  A human somatic cell: Is a typical body cell Has 46 chromosomes  A karyotype is an image that reveals an orderly arrangement of chromosomes.  Homologous chromosomes are matching pairs of chromosomes that can possess different versions of the same genes.

49. Pair of homologous chromosomes LM One duplicated chromosome Centromere Sister chromatids Figure 8.11

50. Human Chromosomes  Humans have: Two different sex chromosomes, X and Y Twenty-two pairs of matching chromosomes, called autosomes  Humans are diploid organisms in which: Their somatic cells contain two sets of chromosomes Their gametes are haploid, having only one set of chromosomes

51. Gametes and the Life Cycle of a Sexual Organism  The life cycle of a multicellular organism is the sequence of stages leading from the adults of one generation to the adults of the next.

52. Multicellular diploid adults (2n  46) MEIOSIS FERTILIZATION MITOSIS 2n2n and development Key Sperm cell n n Diploid zygote (2n  46) Diploid (2n) Haploid (n) Egg cell Haploid gametes (n  23) Figure 8.12

53. Meiosis  Humans are diploid organisms in which: Their somatic cells contain two sets of chromosomes Their gametes are haploid, having only one set of chromosomes  In humans, a haploid sperm fuses with a haploid egg during fertilization to form a diploid zygote.  Sexual life cycles involve an alternation of diploid and haploid stages.  Meiosis produces haploid gametes, which keeps the chromosome number from doubling every generation.

54. MEIOSIS I Sister chromatids separate. MEIOSIS II Homologous chromosomes separate. INTERPHASE BEFORE MEIOSIS Sister chromatids Duplicated pair of homologous chromosomes Chromosomes duplicate. Pair of homologous chromosomes in diploid parent cell Figure 8.13-3

55. The Process of Meiosis  In meiosis: Haploid daughter cells are produced in diploid organisms Interphase is followed by two consecutive divisions, meiosis I and meiosis II Crossing over occurs

56. MEIOSIS I: HOMOLOGOUS CHROMOSOMES SEPARATE Sister chromatids remain attached Pair of homologous chromosomes INTERPHASE Sister chromatids Homologous chromosomes pair up and exchange segments. Chromosomes duplicate. Pairs of homologous chromosomes line up. Pairs of homologous chromosomes split up. Nuclear envelope Chromatin Centromere Microtubules attached to chromosome Sites of crossing over Spindle Centrosomes (with centriole pairs) PROPHASE IMETAPHASE I ANAPHASE I Figure 8.14a

57. TELOPHASE II AND CYTOKINESIS Sister chromatids separate ANAPHASE II Cleavage furrow TELOPHASE I AND CYTOKINESIS Two haploid cells form; chromosomes are still doubled. MEIOSIS II: SISTER CHROMATIDS SEPARATE PROPHASE IIMETAPHASE II During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes. Haploid daughter cells forming Figure 8.14b

58. LM Figure 8.14bc

59. Review: Comparing Mitosis and Meiosis  In mitosis and meiosis, the chromosomes duplicate only once, during the preceding interphase.  The number of cell divisions varies: Mitosis uses one division and produces two diploid cells Meiosis uses two divisions and produces four haploid cells  All the events unique to meiosis occur during meiosis I, while meiosis II is the same as mitosis since it separates sister chromatids.

60. Duplicated chromosome (two sister chromatids) MITOSIS Prophase Chromosome duplication Chromosomes align at the middle of the cell. Metaphase Sister chromatids separate during anaphase. Anaphase Telophase Daughter cells of mitosis 2n2n 2n2n Prophase I Metaphase I Anaphase I Telophase I MEIOSIS Chromosome duplication Homologous chromosomes come together in pairs. MEIOSIS I Site of crossing over between homologous (nonsister) chromatids Homologous pairs align at the middle of the cell. Chromosome with two sister chromatids Homologous chromosomes separate during anaphase I; sister chromatids remain together. Daughter cells of meiosis I Sister chromatids separate during anaphase II. Haploid n  2 MEIOSIS II Parent cell (before chromosome duplication) 2n  4 Daughter cells of meiosis II n n n n Figure 8.15

61. Independent Assortment of Chromosomes  When aligned during metaphase I of meiosis, the side- by-side orientation of each homologous pair of chromosomes is a matter of chance.  Every chromosome pair orients independently of the others during meiosis.  For any species the total number of chromosome combinations that can appear in the gametes due to independent assortment is: 2 n where n is the haploid number.  For a human: n = 23 2 23 = 8,388,608 different chromosome combinations possible in a gamete

62. Metaphase of meiosis I Metaphase of meiosis II Combination a POSSIBILITY 1 POSSIBILITY 2 Combination bCombination c Combination d Gametes Figure 8.16-3

63. Random Fertilization  A human egg cell is fertilized randomly by one sperm, leading to genetic variety in the zygote.  If each gamete represents one of 8,388,608 different chromosome combinations, at fertilization, humans would have 8,388,608 × 8,388,608, or more than 70 trillion, different possible chromosome combinations.

64. Figure 8.17

65. Crossing Over  In crossing over: Homologous chromosomes exchange genetic information Genetic recombination, the production of gene combinations different from those carried by parental chromosomes, occurs

66. Metaphase I Metaphase II Recombinant chromosomes Gametes Recombinant chromosomes combine genetic information from different parents. Homologous chromatids exchange corresponding segments. Sister chromatids remain joined at their centromeres. Prophase I of meiosis Duplicated pair of homologous chromosomes Chiasma, site of crossing over Spindle microtubule Figure 8.18-5

67. How Accidents during Meiosis Can Alter Chromosome Number  In nondisjunction, the members of a chromosome pair fail to separate during anaphase, producing gametes with an incorrect number of chromosomes.  Nondisjunction can occur during meiosis I or II.  If nondisjunction occurs, and a normal sperm fertilizes an egg with an extra chromosome, the result is a zygote with a total of 2n + 1 chromosomes.  If the organism survives, it will have an abnormal number of genes.

68. Meiosis I Abnormal gametes Gametes Nondisjunction: Pair of homologous chromosomes fails to separate. NONDISJUNCTION IN MEIOSIS I Number of chromosomes Meiosis II Nondisjunction: Pair of sister chromatids fails to separate. Abnormal gametes Normal gametes n n n  1 n – 1 n  1 NONDISJUNCTION IN MEIOSIS II n – 1 Figure 8.20-3

69. Abnormal egg cell with extra chromosome Normal sperm cell n  1 n (normal) Abnormal zygote with extra chromosome 2n  1 Figure 8.21

70. Down Syndrome  Down Syndrome: Is also called trisomy 21 Is a condition in which an individual has an extra chromosome 21 Affects about one out of every 700 children The incidence of Down Syndrome increases with the age of the mother.

71. Chromosome 21 LM Figure 8.22

72. Age of mother 25 35 45 20 30 40 50 10 0 20 30 40 50 60 70 80 90 Infants with Down syndrome (per 1,000 births) Figure 8.23

73. Abnormal Numbers of Sex Chromosomes  Nondisjunction can also affect the sex chromosomes.

74. Table 8.1

75. Evolution Connection: The Advantages of Sex  Asexual reproduction conveys an evolutionary advantage when plants are: Sparsely distributed Superbly suited to a stable environment  Sexual reproduction may convey an evolutionary advantage by: Speeding adaptation to a changing environment Allowing a population to more easily rid itself of harmful genes

76. Figure 8.24

77. Duplication of all chromosomes Genetically identical daughter cells Distribution via mitosis Figure 8.UN1

78. Interphase Cell growth and chromosome duplication G2G2 Mitotic (M) phase S phase DNA synthesis; chromosome duplication G1G1 Genetically identical “daughter” cells Cytokinesis (division of cytoplasm) Mitosis (division of nucleus) Figure 8.UN3

79. MITOSIS Male and female diploid adults (2n  46) MEIOSIS Sperm cell Human Life Cycle Key Haploid (n) Diploid (2n) Haploid gametes (n  23) Egg cell Diploid zygote (2n  46) and development FERTILIZATION 2n2n n n Figure 8.UN4

80. Daughter cells Parent cell (2n) MITOSIS Chromosome duplication 2n2n2n2n MEIOSIS MEIOSIS I Parent cell (2n) Chromosome duplication Daughter cells n MEIOSIS II Pairing of homologous chromosome Crossing over n nn Figure 8.UN5

81. Differences between Mitosis and Meiosis Meiosis has 2 divisions – two rounds of chromosome separation. Crossing over in meiosis – exchange of genetic material between homologous chromosomes – occurs during synapsis(pairing of homologous chromosomes in M I)

82. Differences between Mitosis and Meiosis Mitosis occurs in all cells, meiosis limited to certain cells Mitosis produces 2 identical cells, Meiosis produce 4 cells which are not identical Mitosis : daughter cells of same ploidy as parent; Meiosis: daughter cells haploid of parent

83. (a) LM (b) (c) (d) Figure 8.UN6