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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 15 LECTURE SLIDES Prepared by Brenda Leady University.

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Presentation on theme: "Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 15 LECTURE SLIDES Prepared by Brenda Leady University."— Presentation transcript:

1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 15 LECTURE SLIDES Prepared by Brenda Leady University of Toledo To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please note: once you have used any of the animation functions (such as Play or Pause), you must first click in the white background before you advance the next slide.

2 Cell division Reproduction of cells Highly regulated series of events 2 types in eukaryotes  Mitosis  Meiosis 2

3 3 Cell cycle G 1 – first gap unduplicated chromosomes S – synthesis of DNA Interphase G 2 – second gap M – mitosis and cytokinesis G 0 – substitute for G 1 for cells postponing division or never dividing again 3

4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. S M G2G2 G1G1 Interphase Cytokinesis Telophase Anaphase Metaphase Prometaphase Prophase 4

5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. S M G2G2 G1G1 Interphase Cytokinesis Telophase Anaphase Metaphase Prometaphase Prophase 5

6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. S M G2G2 G1G1 Interphase Cytokinesis Telophase Anaphase Metaphase Prometaphase Prophase 6

7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. S M G2G2 G1G1 Interphase Cytokinesis Telophase Anaphase Metaphase Prometaphase Prophase 7

8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Two daughter cells form, each containing 6 chromosomes. S M G2G2 G1G1 Interphase Cytokinesis Telophase Anaphase Metaphase Prometaphase Prophase 8

9 G 1 phase Cell accumulates molecular changes that cause progression through the cell cycle Passes restriction point where cell is committed to enter S phase Chromosomes replicate during S phase forming sister chromatids 9

10 S phase Chromosomes replicate After replication, 2 copies stay joined to each other and are called sister chromatids Human cell in G 1 has 46 chromosomes  Same cell in G 2 (after S) has 46 pairs of sister chromatids or 92 chromatids 10

11 11

12 G 2  Cell synthesizes proteins needed during mitosis and cytokinesis M phase – mitosis  Divide one cell nucleus into two Cyokinesis  Division of cytoplasm, follows in most cases 12

13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Activated G 1 cyclin/cdk complex Mitotic cyclin cdk G 1 cyclin G 1 cyclin is degraded after cell enters S phase. Activated mitotic cyclin/cdk complex Mitotic cyclin is degraded as cell progresses through mitosis. S M G2G2 G1G1 13

14 14 3 critical regulatory points or checkpoints in eukaryotes  G 1 checkpoint (restriction point)  G 2 checkpoint  Metaphase checkpoint Checkpoint proteins act as sensors to determine if the cell is in proper condition to divide Cell cycle will be delayed or until problems fixed or prevents division entirely Loss of checkpoint function can lead to mutation and cancer 14

15 15 Mitotic cell division A cell divides to produce 2 new cells genetically identical to the original Original called mother, new cells called daughters Involves mitosis and cytokinesis Can be for asexual reproduction or for production and maintenance of multicellularity

16 16 Preparation for cell division DNA replicated Sister chromatids - 2 identical copies with associated proteins Tightly associates at centromere Serves as attachment site for kinetochore used in sorting chromosomes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Kinetochore Pair of sister chromatids Sister chromatids (a) Chromosome replication and compaction (b) Schematic drawing of a metaphase chromosome Centromere (a region of DNA beneath kinetochore proteins) One chromatid One chromatid

17 17 Mitotic spindle Sorting process that ensures that each daughter cell will obtain the correct number and types of chromosomes Mitotic spindle apparatus (or mitotic spindle) is responsible for organizing and sorting the chromosomes during mitosis Composed of microtubules

18 18 Animal cell mitotic spindle Centrosomes  Microtubule organizing center (MTOCs) Single centrosome duplicates at the beginning of M phase Each defines a pole Animal cells have centrioles  Not found in many other eukaryotes

19 19 Interphase - phase of the cell cycle during which the chromosomes are decondensed and found in the nucleus Mitosis  Prophase  Prometaphase  Metaphase  Anaphase  Telophase Cytokinesis

20 20 Prophase Chromosomes have already replicated to produce 12 chromatids, joined as six pairs of sister chromatids Nuclear membrane dissociates into small vesicles Chromatids condense into highly compacted structures that are readily visible by light microscopy

21 21 Prometaphase Nuclear envelope completely fragments Mitotic spindle is fully formed during this phase Centrosomes move apart and demarcate the two poles Spindle fibers interact with sister chromatids Two kinetochores on each pair of sister chromatids are attached to kinetochore microtubules from opposite poles

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23 23 Metaphase Pairs of sister chromatids are aligned along a plane halfway between the poles called the metaphase plate Organized into a single row When this alignment is complete, the cell is in metaphase

24 24 Anaphase Connections between the pairs of sister chromatids are broken Each chromatid, now an individual chromosome, is linked to only one of the two poles by one or more kinetochore microtubules Kinetochore microtubules shorten, pulling the chromosomes toward the pole to which they are attached Two poles move farther away from each other as overlapping polar microtubules lengthen and push against each other

25 25 Telophase Chromosomes have reached their respective poles and decondense Nuclear membranes now re-form to produce two separate nuclei

26 26

27 27 Cytokinesis In most cases, mitosis is quickly followed by cytokinesis Two nuclei are segregated into separate daughter cells Process of cytokinesis is quite different in animals and plants  Animals - cleavage furrow constricts like a drawstring to separate the cells  Plants - cell plate forms a cell wall between the two daughter cells

28 28

29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cleavage furrow Contractile ring Central spindle

30 30 Meiosis Sexual reproduction requires a fertilization event in which two haploid gametes unite to create a diploid cell called a zygote Meiosis is the process by which haploid cells are produced from a cell that was originally diploid

31 31 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G 1 phase prior to meiosis Homologous pair of chromosomes prior to chromosomal replication A diploid cell

32 32 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Meiosis I Sister chromatids G 1 phase prior to meiosis Homologous pair of chromosomes prior to chromosomal replication A diploid cell Diploid cell with replicated and condensed chromosomes

33 33 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Meiosis I Sister chromatids G 1 phase prior to meiosis Homologous pair of chromosomes prior to chromosomal replication A diploid cell Diploid cell with replicated and condensed chromosomes Haploid cells with pairs of sister chromatids

34 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Meiosis I Meiosis II Sister chromatids 4 haploid cells with individual chromosomes G 1 phase prior to meiosis Homologous pair of chromosomes prior to chromosomal replication A diploid cell Diploid cell with replicated and condensed chromosomes Haploid cells with pairs of sister chromatids 34

35 35 Like mitosis, meiosis begins after a cell has progressed through the G1, S, and G2 phases of the cell cycle 2 key differences 1. Homologous pairs form a bivalent or tetrad 2. Crossing over

36 36 Bivalent or tetrad Homologous pairs of sister chromatids associate with each other, lying side by side to form a bivalent or tetrad Process called synapsis Synaptonemal complex not required for pairing of homologous chromosomes

37 37 Crossing over Physical exchange between chromosome pieces of the crossing bivalent May increase the genetic variation of a species Chiasma - arms of the chromosomes tend to separate but remain adhered at a crossover site Number of crossovers carefully controlled by cells

38 Synaptonemal complex forming Bivalent Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 38

39 Chiasma Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Synaptonemal complex forming Bivalent 39

40 40 Meiosis I Prophase I - replicated chromosomes condense and bivalents form as the nuclear membrane breaks down Prometaphase I - spindle apparatus complete, and the chromatids are attached to kinetochore microtubules  Pairs of sister chromatids attached to 1 pole Metaphase I - bivalents organized along metaphase plate as double row  Mechanism to promote genetic diversity

41 41 Anaphase I - segregation of homologues occurs  Connections between bivalents break, but not the connections that hold sister chromatids together  Each joined pair of chromatids migrates to one pole, and the homologous pair of chromatids moves to the opposite pole Telophase I - sister chromatids have reached their respective poles and decondense and nuclear membranes reform Cytokinesis Original diploid cell had its chromosomes in homologous pairs, while the two cells produced at the end of meiosis I are haploid - they do not have pairs of homologous chromosomes

42 42 Meiosis II No S phase between meiosis I and meiosis II Sorting events of meiosis II are similar to those of mitosis Sister chromatids are separated during anaphase II, unlike anaphase I

43 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (c) Metaphase I(b) Prometaphase I CentrosomeSpindle forming Bivalent Meiosis I Meiosis II (a) Prophase I (g) Prometaphase II(f) Prophase II(h) Metaphase II Metaphase plate Sister chromatids (e) Telophase I and cytokinesis (d) Anaphase I (i) Anaphase II Cleavage furrow 43

44 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (c) Metaphase I(b) Prometaphase I CentrosomeSpindle forming Bivalent Meiosis I Meiosis II (a) Prophase I (g) Prometaphase II(f) Prophase II(h) Metaphase II Metaphase plate Sister chromatids 44

45 (e) Telophase I and cytokinesis (d) Anaphase I (i) Anaphase II(j) Telophase II and cytokinesis Four haploid cells Cleavage furrow Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 45

46 46 Meiosis vs. Mitosis Mitosis produces two diploid daughter cells that are genetically identical  6 chromosomes in 3 homologous pairs Meiosis produces four haploid daughter cells  Each daughter has a random mix of 3 chromosomes

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48 48 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

49 49 Life Cycle Sequence of events that produces another generation of organisms For sexually reproducing organisms, involves an alternation between haploid cells or organisms and diploid cells or organisms

50 50 Diploid-dominant species  Most animal species are diploid  Haploid gametes are a specialized type of cell Haploid-dominant species  Many fungi and some protists  Multicellular organism is haploid  Haploid cells unite to form diploid zygote, then proceeds immediately through meiosis to make 4 haploid spores

51 51 Alternation of generations  Plants and some algae  Intermediate dominance  Multicellular diploid organism – sporophyte  Multicellular haploid organism – gametophyte  Among species, relative size of sporophyte and gametophyte varies

52 52

53 53 Variation in Chromosomes Chromosome composition within a given species tends to remain relatively constant  Humans - 2 sets of 23 chromosomes (total of 46)  Dog - 78 chromosomes (39 per set)  Fruit fly - 8 chromosomes (4 per set)  Tomato - 24 chromosomes (12 per set)

54 54 Chromosomes identified by  Size  Location of centromere Short arm is p, long arm is q, short arms on top Metacentric – middle Submetacentric – off center Acrocentric – near end Telocentric – at the end  Banding pattern Giemsa stain gives G banding

55 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. AcrocentricMetacentricSubmetacentric p q p q p q p q Telocentric 55

56 56 Chromosomal mutations Deletions  Segment missing Duplications  Section occurs 2 or more times in a row Inversions  Change in direction along a single chromosome Translocations  One segment becomes attached to another chromosome  Simple or reciprocal

57 57 Changes in chromosome number Euploid - chromosome number that is viewed as the normal number  In a diploid organism, 2 sets is normal Polyploid - 3 or more sets of chromosomes  Diploid 2n  Triploid 3n  Tetraploid 4n

58 58


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