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CHAPTER 15 LECTURE SLIDES

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1 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. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

3 Cell cycle G1 – first gap unduplicated chromosomes
S – synthesis of DNA Interphase G2 – second gap M – mitosis and cytokinesis G0 – substitute for G1 for cells postponing division or never dividing again 3

4 Mitosis S G1 G2 M Interphase Cytokinesis Prophase Telophase
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. S Interphase G1 G2 M Mitosis Cytokinesis Prophase Telophase Anaphase Metaphase Prometaphase 4

5 Mitosis S G1 G2 M 5 Interphase Cytokinesis Prophase Telophase
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. S Interphase G1 G2 M Mitosis Cytokinesis Prophase Telophase Anaphase Metaphase Prometaphase 5

6 Mitosis S G1 G2 Interphase M 6 Cytokinesis Telophase Prophase Anaphase
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. S Interphase G1 G2 M Mitosis Cytokinesis Telophase Prophase Anaphase Metaphase Prometaphase 6

7 Mitosis S G1 G2 7 Interphase M
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. S Interphase G1 G2 M Mitosis Cytokinesis Telophase Prophase Anaphase Metaphase Prometaphase 7

8 Mitosis S G1 G2 8 Two daughter cells form, each
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. S Interphase G1 G2 M Mitosis Cytokinesis Telophase Prophase Anaphase Metaphase Prometaphase 8 Two daughter cells form, each containing 6 chromosomes.

9 G1 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

10 S phase Chromosomes replicate
After replication, 2 copies stay joined to each other and are called sister chromatids Human cell in G1 has 46 chromosomes Same cell in G2 (after S) has 46 pairs of sister chromatids or 92 chromatids

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12 G2 M phase – mitosis Cyokinesis
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

13 after cell enters S phase.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G1 cyclin is degraded after cell enters S phase. cdk Mitotic cyclin S M G2 G1 Activated G1 cyclin/cdk complex cdk G1 cyclin cdk Activated mitotic cyclin/cdk complex cdk Mitotic cyclin is degraded as cell progresses through mitosis. 13

14 3 critical regulatory points or checkpoints in eukaryotes
G1 checkpoint (restriction point) G2 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 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 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 Centromere (a region of DNA beneath kinetochore proteins) Sister chromatids One chromatid One chromatid Pair of sister chromatids (a) Chromosome replication and compaction (b) Schematic drawing of a metaphase chromosome

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

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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

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

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 G1 phase prior to meiosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G1 phase prior to meiosis A diploid cell Homologous pair of chromosomes prior to chromosomal replication

32 G1 phase prior to meiosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G1 phase prior to meiosis A diploid cell Homologous pair of chromosomes prior to chromosomal replication Meiosis I Diploid cell with replicated and condensed chromosomes Sister chromatids 32

33 G1 phase prior to meiosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G1 phase prior to meiosis A diploid cell Homologous pair of chromosomes prior to chromosomal replication Meiosis I Diploid cell with replicated and condensed chromosomes Sister chromatids Haploid cells with pairs of sister chromatids 33

34 34 G1 phase prior to meiosis A diploid cell Homologous pair
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G1 phase prior to meiosis A diploid cell Homologous pair of chromosomes prior to chromosomal replication Meiosis I Diploid cell with replicated and condensed chromosomes Sister chromatids Haploid cells with pairs of sister chromatids Meiosis II 34 4 haploid cells with individual chromosomes

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

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

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

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

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

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

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 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 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 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 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

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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 chromosomes (39 per set) Fruit fly - 8 chromosomes (4 per set) Tomato - 24 chromosomes (12 per set)

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

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 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

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