1. © 2013 Pearson Education, Inc. Lectures by Edward J. Zalisko PowerPoint ® Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fourth Edition – Eric J. Simon, Jean L. Dickey, and Jane B. Reece Chapter 8 Cellular Reproduction: Cells from Cells

2. 1) Cell reproduction – Asexual and Sexual 2) Cell cycle and mitosis i. Chromosomes and their organization ii. The different phases of cell cycle iii. Different phases of Mitosis and cytokinesis iv. Cancer cells – out of cell cycle control 3) Meiosis i. Homologous chromosome ii. Life cycle of sexual organism iii. Different phases of Meiosis iv. Origin of genetic variation v. Disorders/diseases - When meiosis goes wrong We will learn

3. WHAT CELL REPRODUCTION ACOMPLISHES Reproduction: –May result in the birth of new organisms –More commonly involves the production of new cells When a cell undergoes reproduction, or cell division, two “daughter” cells are produced that are genetically identical to each other and to the “parent” cell. Before a parent cell splits into two, it duplicates its chromosomes, the structures that contain most of the organism’s DNA. During cell division, each daughter cell receives one set of chromosomes.

4. Cell division plays important roles in the lives of organisms. Cell division: –Replaces damaged or lost cells –Permits growth –Allows for reproduction Function of Mitotic Cell division

6. Cell ReplacementGrowth via Cell Division Human kidney cell Early human embryo LM Colorized SEM Three functions of cell division

7. In asexual reproduction: –Single-celled organisms reproduce by simple cell division –There is no fertilization of an egg by a sperm –The lone parent and its offspring have identical genes Some multicellular organisms, such as sea stars, can grow new individuals from fragmented pieces. Growing a new plant from a clipping is another example of asexual reproduction. WHAT CELL REPRODUCTION ACOMPLISHES

8. In asexual reproduction, the lone parent and its offspring have identical genes. Mitosis is the type of cell division responsible for: –Asexual reproduction –Growth and maintenance of multicellular organisms 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 ( production of gametes ) –Mitosis for growth and maintenance WHAT CELL REPRODUCTION ACOMPLISHES

9. In a eukaryotic cell: –Most genes are located on chromosomes in the cell nucleus  A few genes are found in DNA in mitochondria and chloroplasts –Each eukaryotic chromosome contains one very long DNA molecule, typically bearing thousands of genes. –The number of chromosomes in a eukaryotic cell depends on the species. THE CELL CYCLE AND MITOSIS

10. 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

11. Organization of Eukaryotic Chromosomes Chromosomes: –Are made of chromatin fibers composed of roughly equal amounts of DNA and protein molecules and, –Are not visible in a cell until cell division occurs Condensation of chromosomes into distinct units Chromosomes LM

12. Figure 8.4 Duplicated chromosomes (sister chromatids) TEM Tight helical fiber Thick supercoil TEM Centromere Nucleosome “Beads on a string” Histones DNA double helix The DNA in a cell is packed into an elaborate, multilevel system of coiling and folding. Histones are proteins used to package DNA in eukaryotes. Nucleosomes consist of DNA wound around histone molecules. Organization of Eukaryotic Chromosomes

13. 1.At first level of packing, histones attach to the DNA (the combination looks like bead on a string and each bead is called nucleosome) 2.At second level, the beaded string is wrapped into tight helical fiber 3.At third level, the fiber coils further into supercoils 4.At the last level, looping and folding can further compact the DNA When the cells are not dividing, DNA appears lightly packed, with much of the DNA in ‘bead on string’ nucleosome arrangement When prepares to divide, they pack further Organization of Eukaryotic Chromosomes

14. 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 Chromosome duplication Sister chromatids Chromosome distribution to daughter cells Chromosome duplication and distribution

15. 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 During interphase, a cell: Performs its normal functions Doubles everything in its cytoplasm (organelles, etc) when getting ready to divide ER get busy to ge Ribosome get busy to produce protein Grows in size The cell cycle consists of two distinct phases: 1.Interphase - Most of a cell cycle is spent in interphase 2.Mitotic phase

16. 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 The eukaryotic cell cycle

17. Mitosis and Cytokinesis Mitotic (M) phase includes two overlapping processes: 1.Mitosis, in which the nucleus and its contents divide evenly into two daughter nuclei 2.Cytokinesis, in which the cytoplasm is divided in two During mitosis the mitotic spindle guides the separation of two sets of daughter chromosomes. Spindle microtubules grow from two centrosomes – clouds of cytoplasmic material that in animal cells contain centrioles

18. Mitosis and Cytokinesis Mitosis consists of four distinct phases: 1.Prophase 2.Metaphase 3.Anaphase 4.Telophase.

20. PROPHASE  Chromosomes (each consisting of two sister chromatids) start to condense into discrete chromosomes.  The nucleoli disappear.  The mitotic spindle begins to form  The centrosomes move away from each other,  The nuclear membrane breaks down  The mitotic spindle (made of microtubules ) begins to form and extends from each centrosome and invades the nuclear area

21. 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

22. METAPHASE AND ANAPHASE Metaphase  Chromosomes are fully condensed and most visible at this stage  The sister chromatids are arranged at the metaphase plate, or the equator of the cell, an imaginary plane equal distant from the spindle’s two poles. Anaphase  The sister chromatids separate and move apart and become full-fledged chromosomes.  Each freed chromatid (now referred to as a chromosome or daughter chromosome) is pulled toward the opposite pole of the cell

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

24. TELOPHASE  Each set of chromosomes have reached the opposite pole of the cell  The chromosomes decondense.  The mitotic spindle disappears  Two daughter nuclei begin to form, one at each pole  The nuclear envelope and nucleolus reappear  Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete

25. Cytokinesis typically: –Occurs during telophase –Divides the cytoplasm –Is different in plant and animal cells  In animal cells, cytokinesis involves the formation of a cleavage furrow, which contracts to pinch the cell in two.  In plant cells, small vesicles containing cell wall materials fuse to form a cell plate, which grows outwards to complete the formation of two daughter cells. CYTOKINESIS

27. Cleavage furrow Contracting ring of microfilaments Daughter cells New cell wall Vesicles containing cell wall material Cell plate Cell wall Wall of parent cell Cell plate forming Daughter nucleus LM Cytokinesis in plant cells Cytokinesis in animal cells

28. 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. Cancer is a disease of the cell cycle, that do not respond normally to the cell cycle control system. Cancer cells can form tumors, abnormally growing masses of body cells. If the abnormal cells remain at the original site, the lump is called a benign tumor.

29. Cancer Cells: Growing Out of Control 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 A person with a malignant tumor is said to have cancer.

30. 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 Growth and metastasis of a malignant tumor of the breast

31. Cancer Treatment and Prevention Cancer treatment can involve: Radiation therapy, which damages DNA and disrupts cell division Chemotherapy, which uses drugs that disrupt cell division by interfering with mitotic spindle

32. Cancer Treatment and Prevention 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

33. What is the difference between a benign and a malignant tumor? A) Benign tumors are composed of cancer cells; malignant tumors are not. B) Benign tumors cannot kill you; malignant tumors can. C) Benign tumors are not the result of a failure of a cell cycle control system; malignant tumors are. D) Benign tumors do not metastasize; malignant tumors do. E) Benign tumors do not form lumps; malignant tumors do form lumps.

34. A chemical that disrupts microfilament formation would interfere with A) DNA replication. B) Formation of the mitotic spindle. C) Cleavage. D) Crossing over

35. Sexual reproduction ( is important because it introduce such unique combination and also variation ): –Uses meiosis –Uses fertilization –Produces offspring that contain a unique combination of genes from the parents Meiosis, the Basis of Sexual Reproduction © 2010 Pearson Education, Inc.

36. Figure 8.10

37. Different individuals of a single species have the same number and types of chromosomes. Human somatic cell is a typical body cell –All body cells except for the gametes (egg and sperm) has 46 chromosomes (23 pairs) 22 pairs of matching chromosomes, called autosomes –Humans have two different sex chromosomes, X and Y Homologous chromosomes are matching pairs of chromosomes has same gene in the same position on the chromosome but possess different versions of the same genes. Homologous Chromosomes

38. Pair of homologous chromosomes LM One duplicated chromosome Centromere Sister chromatids A karyotype is an image that reveals an orderly arrangement of chromosomes.

39. 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. 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)

40. 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. Gametes and the Life Cycle of a Sexual Organism

41. Figure 8.13-3 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 1 2 3 How meiosis halves chromosome number

42. The Process of Meiosis In meiosis, –Haploid daughter cells are produced from diploid cells –The number of chromosome is reduced to half –Involves two consecutive divisions, meiosis I and meiosis II that occur after interphase –There is an exchange of genetic material – pieces of chromosomes- between the homologous chromosome. This exchange of chromosome is called crossing over

43. 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

44. 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

46. 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 identical diploid cells –Meiosis uses two divisions and produces four non-identical haploid cells All the events unique to meiosis occur during meiosis I.

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

48. SUMMARY PropertyMitosis Meiosis DNA replication Number of divisions Synapsis of homologous chromosomes Number of daughter cells and genetic composition Role in the animal body

49. SUMMARY PropertyMitosis Meiosis DNA replication Number of divisions Synapsis of homologous chromosomes Number of daughter cells and genetic composition Role in the animal body Occurs during interphase before mitosis begins One, including prophase, metaphase, anaphase, and telophase Does not occur Two, each diploid (2n) and genetically identical to the parent cell Enables multicellular adult to arise from zygote; produces cells for growth, repair, &, in some species, asexual reproduction Occurs during interphase before meiosis I begins Two, each including prophase, metaphase, anaphase, and telophase Occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion Four, each haploid (n), containing half as many chromosomes as the parent cell; genetically different from the parent cell and from each other Produces gametes; reduces number of chromosomes by half and introduces genetic variability among the gametes

50. The Origins of Genetic Variation Offspring of sexual reproduction are genetically different from their parents and one another. 1.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.

51. Figure 8.16-3 Two equally probable arrangements of chromosomes at metaphase of meiosis I Metaphase of meiosis II Combination a POSSIBILITY 1 POSSIBILITY 2 Combination bCombination c Combination d Gametes Because possibilities 1 and 2 are equally likely, the four possible types of gametes will be made in approximately equal numbers.

52. 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 Independent Assortment of Chromosomes

53. 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. So we see that the random nature of fertilization adds a huge amount of potential variability to the offspring of sexual reproduction. 2. Random Fertilization

54. –nonsister chromatids of homologous chromosomes exchange genetic information –Genetic recombination, the production of gene combinations different from those carried by parental chromosomes, occurs 3. Crossing over

55. 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

57. What happens when errors occur in meiosis? Such mistakes can result in genetic abnormalities that range from mild to fatal. When Meiosis Goes Awry

58. 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 karyotype and – probably a syndrome of disorders caused by the abnormal number of genes When Meiosis Goes Awry

59. Abnormal egg cell with extra chromosome Normal sperm cell n  1 n (normal) Abnormal zygote with extra chromosome 2n  1 Fertilization after nondisjunction in the mother

60. Down Syndrome: An Extra Chromosome 21 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. Chromosome 21

61. Meiosis I Nondisjunction: Pair of homologous chromosomes fails to separate. NONDISJUNCTION IN MEIOSIS I NONDISJUNCTION IN MEIOSIS II Figure 8.20-1

62. Meiosis I Nondisjunction: Pair of homologous chromosomes fails to separate. NONDISJUNCTION IN MEIOSIS I Meiosis II Nondisjunction: Pair of sister chromatids fails to separate. NONDISJUNCTION IN MEIOSIS II Figure 8.20-2

63. 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 Two types of nondisjunction

64. Abnormal Numbers of Sex Chromosomes Nondisjunction in meiosis –can lead to abnormal numbers of sex chromosomes but –seems to upset the genetic balance less than unusual numbers of autosomes, perhaps because the Y chromosome is very small and carries relatively few genes. © 2013 Pearson Education, Inc.

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

66. Evolution Connection: The Advantages of Sex Asexual reproduction conveys an evolutionary advantage when plants are –sparsely distributed and unlikely to be able to exchange pollen or –superbly suited to a stable environment. Asexual reproduction also eliminates the need to expend energy –forming gametes and –copulating with a partner. © 2013 Pearson Education, Inc.

67. Sexual reproduction may convey an evolutionary advantage by –speeding adaptation to a changing environment or –allowing a population to more easily rid itself of harmful genes. Evolution Connection: The Advantages of Sex © 2013 Pearson Education, Inc.

68. Figure 8.24 Runner

69. The Process of Science: Do All Animals Have Sex? Observation: No scientists have ever found male bdelloid rotifers, a microscopic freshwater invertebrate. Question: Does this entire class of animals reproduce solely by asexual means? Hypothesis: Bdelloid rotifers have thrived for millions of years despite a lack of sexual reproduction. Prediction: Bdelloid rotifers would display much more variation in their pairs of homologous genes than most organisms. Experiment: Researchers compared sequences of a particular gene in bdelloid and non-bdelloid rotifers.

70. Results: –Non-bdelloid sexually reproducing rotifers had a nearly identical homologous gene, differing by only 0.5% on average. –The two versions of the same gene in asexually reproducing bdelloid rotifers differed by 3.5–54%. Conclusion: Bdelloid rotifers have evolved for millions of years without any sexual reproduction. The Process of Science: Do All Animals Have Sex?

71. Figure 8.19 LM

72. Figure 8.7.aa