AP Biology Day 47. Wednesday, January 11, 2017

Transcription

1 AP Biology Day 47 Wednesday, January 11, 2017

2 Do-Now 1. Turn in break HW to box à must be complete (every ques8on a9empted). 2. Turn in Unit Logs to box 3. Labs turned in by neatly stacking them on the back table 4. Have out your unit logs, planners, and Ch. 13 Notes Outline

3 CW/HW Assignments 1. Ch. 13 Lecture Notes 2. Ch. 13 Video Cornell Notes (2) 3. Ch. 14 Guided Reading PLANNER Complete Ch. 13 VCN (2) tonight Complete Ch. 14 GR by Friday Ch. 13 Quiz

4 EssenFal knowledge standards 3.A.2: In eukaryotes, heritable informa8on is passed to the next genera8on via processes that include the cell cycle and mitosis or meiosis plus fer8liza8on. 3.C.2: Biological systems have mul8ple processes that increase gene8c varia8on.

5 I will be able to: FLT describe the events that characterize each phase of meiosis disfnguish between the following terms: somafc cell and gamete; autosome and sex chromosomes; haploid and diploid Name and explain the three events that contribute to genefc variafon in sexually reproducing organisms By comple1ng Ch. 13 Lecture Notes

6 Ch. 13: Meiosis & Sexual Life Cycles

7 Recap 7

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9 DNA vs. Chromosomes 9

10 Mitosis 10

11 FerFlizaFon 11

12 SomaFc Cells vs. Gametes 12

13 Homologous Chromosomes 13

14 Autosomes vs. Sex Chromosomes 14

15 III. Sexual Life Cycles 15

16 Meiosis Overview 16

17 Meiosis Occurs in the gonads (ovaries and testes) Reduces the chromosome number by half (2n à n) Produces haploid gametes Fer8liza8on (n+n) restores the normal chromosome number. 17

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20 Human Life Cycle Key Haploid gametes (n = 23) Haploid (n) Egg (n) Diploid (2n) Sperm (n) MEIOSIS FERTILIZATION Ovary Tes8s Diploid zygote (2n = 46) Mitosis and development Mul8cellular diploid adults (2n = 46)

21 Pair-Share-Respond 1. Dis8nguish between the terms haploid + diploid. 2. What kind of cells would be haploid and what kind diploid? 3. Explain how meiosis and fer8liza8on work together to maintain a constant number of chromosomes 4. Dis8nguish between spermatogenesis and oogenesis.

22 IV. Meiosis Like mitosis, meiosis is preceded by the replicafon of chromosomes. Meiosis takes place in two sets of cell divisions, called meiosis I and meiosis II. Reduc8on Division 2n --> n. Meiosis has two cell divisions and results in four daughter cells. Each daughter cell has only half as many chromosomes as the parent cell. 22

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24 IV. Meiosis 1 st Division = meiosis I Homologous chromosomes separate Two daughter cells are produced ReducFon division 2 nd Division = meiosis II Results in four haploid daughter cells EquaFonal Division 24

25 Fig Meio8c Cell Division: Interphase Homologous pair of chromosomes in diploid parent cell Reduc8on Division Chromosomes replicate Homologous pair of replicated chromosomes 2n-->n Meiosis I Sister chroma8ds Diploid cell with replicated chromosomes Meiosis II 1 Homologous chromosomes separate Haploid cells with replicated chromosomes 2 Sister chroma8ds separate Haploid cells with unreplicated chromosomes

26 IV. Meiosis Interphase = chromosomes are replicated to form sister chromafds = occurs before meiosis I The sister chromafds are genefcally idenfcal and joined at the centromere. The single centrosome replicates, forming two centrosomes. 26

27 IV. Meiosis A. Stages of Meiosis I Division in meiosis I occurs in four phases: Prophase I: synapsis / crossing -over Metaphase I: random alignment at equator Anaphase I: independent assortment homologous chromosomes separate Telophase I and cytokinesis 27

28 Fig. 13-8a Meiosis I: Variety Increases Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Sister chromatids Centrosome (with centriole pair) Chiasmata Spindle Centromere (with kinetochore) Metaphase plate Sister chromatids remain attached Homologous chromosomes Fragments of nuclear envelope Microtubule attached to kinetochore Homologous chromosomes separate Cleavage furrow

29 Prophase I: Synapsis + Crossing Over Synapsis = homologous chromosomes loosely align gene by gene. Tetrad = paired up homologs 29

30 IV. Meiosis Prophase I: Synapsis + Crossing Over Crossing over = nonsister chroma8ds exchange DNA segments, which can create gene0c varia0on. Each tetrad usually has one or more chiasmata, X- shaped regions where crossing over occurred. 30

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33 IV. Meiosis Metaphase I: Random Alignment at Middle In metaphase I, tetrads line up randomly at the metaphase plate (middle), with one chromosome facing each pole. Microtubules from one pole are adached to the kinetochore of one chromosome of each tetrad. Microtubules from the other pole are adached to the kinetochore of the other chromosome. 33

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35 IV. Meiosis Anaphase I: Separa8on of Homologous Pairs In anaphase I, pairs of homologous chromosomes separate. One chromosome moves toward each pole, guided by the spindle apparatus: depolymerizafon of the spindle fibers/ microtubules. Sister chromafds remain adached at the centromere and move as one unit toward the pole. 35

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37 IV. Meiosis Telophase I and Cytokinesis: In the beginning of telophase I, each half of the cell has a haploid set of chromosomes; each chromosome sfll consists of two sister chromafds Cytokinesis usually occurs simultaneously, forming two haploid daughter cells. 37

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39 IV. Meiosis Animal cells à cleavage furrow (acfn) forms Plant cells à cell plate (Golgi vesicles - membrane) forms. 39

40 Meiosis I 40

41 IV. Meiosis No chromosome replicafon occurs between the end of meiosis I and the beginning of meiosis II because the chromosomes are already replicated. 41

42 IV. Meiosis B. Stages of Meiosis II very similar to mitosis 1. Prophase II nuclear envelope breaks down 2. Metaphase II chromosomes line up at plate 3. Anaphase II sister chromafds separate 4. Telophase II/Cytokinesis new nuclei form and cytokinesis occurs 42

43 Fig. 13-8d Meiosis II: Sister Chroma8ds Separate --> 4 Haploid Cells Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis Sister chroma8ds separate Haploid daughter cells forming

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45 IV. Meiosis Cytokinesis separates the cytoplasm. End of meiosis à 4 gene8cally unique haploid (n) daughter cells Meiosis: VARIETY increases with reduc8on division 2n-->n. 45

46 V. Comparing Mitosis and Meiosis A. Mitosis Asexual reproduc8on Produces 2 gene8cally iden8cal daughter cells Chromosome # stays the same (2n à 2n) Can occur in all organisms 46

47 V. Comparing Mitosis and Meiosis B. Meiosis Increases gene8c diversity through sexual reproduc8on Produces 4 gene8cally unique haploid daughter cells Reduces the chromosome number by half Creates gametes 47

48 V. Comparing Mitosis and Meiosis C. SimilariFes The mechanism for separafng sister chromafds is virtually idenfcal in meiosis II and mitosis. 48

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51 VI. Events Unique to Meiosis A. At Prophase I - synapsis + crossing over B. At Metaphase I random assortment of homologs at metaphase plate C. At Anaphase I separafon of homologs 51

52 Pair-Share-Respond 1. What are the results of meiosis (overall)? 2. Describe, specifically, what occurs in prophase I of meiosis. 3. When do homologous chromosomes separate? 4. When do sister chroma8ds separate? 5. Iden8fy three differences between meiosis and mitosis

53 VII. Origins of GeneFc VariaFon Among Offspring Muta8ons (changes in an organism s DNA) are the original source of genefc diversity. MutaFons create different versions of genes called alleles. Sexual Reproduc8on/Recombina8ons - reshuffling of alleles during sexual reproducfon produces genefc variafon 53

54 VII. Origins of GeneFc VariaFon Among Offspring Three mechanisms in Sexual Reproduc0on contribute to genefc variafon: Independent assortment of chromosomes at equator of Metaphase I. Crossing over - Prophase I: synapsis / tetrad Random fer8liza8on The number of combina8ons possible when chromosomes assort independently into gametes is 2 n, where n is the haploid number. For humans (n = 23), there are more than 8 million (2 23 ) possible combinafons of chromosomes. 54

55 Fig Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Combina8on 1 Combina8on 2 Combina8on 3 Combina8on 4

56 VII. Origins of GeneFc VariaFon Among Offspring Crossing over produces recombinant chromosomes, which combine genes inherited from each parent. Crossing over begins very early in prophase I, as homologous chromosomes pair up gene by gene. In crossing over, homologous porfons of two nonsister chromafds trade places. Crossing over contributes to genefc variafon by combining DNA from two parents into a single chromosome. 56

57 Fig Prophase I of meiosis Pair of homologs Chiasma Nonsister chroma8ds held together during synapsis TEM Anaphase I Centromere Anaphase II Daughter cells Recombinant chromosomes

58 VII. Origins of GeneFc VariaFon Among Offspring Random ferflizafon adds to genefc variafon because any sperm can fuse with any ovum (unferflized egg). The fusion of two gametes (each with 8.4 million possible chromosome combinafons from independent assortment) produces a zygote with any of about 70 trillion diploid combinafons. 58

59 VIII. EvoluFonary Significance of GeneFc VariaFon Within PopulaFons Natural selecfon results in the accumulafon of genefc variafons favored by the environment. Sexual reproducfon contributes to the genefc variafon in a populafon, which originates from mutafons. 59

60 HW Finish Ch. 13 Notes Ch. 14 Guided Reading Ch. 13 Video Cornell Notes (2) Ch. 13 Quiz next class! 60