Intitial Question: How can the mathematically impossible become the biologically possiblenamely,

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2 Intitial Question: How can the mathematically impossible become the biologically possiblenamely, a cell with 46 chromosomes splits to form tow cells each with 46 chromosomes/ This means 46 divided by 2 equals 46 plus 46. what event during the cell cycle makes this possible? OBJECTIVES: Describe the events that occur during meiosis Based on the steps of meiosis, conclude why meiosis leads to genetic diversity STANDARDS: Bio.B A4

3 Sexual Reproduction Chromosomes are duplicated in germ cells Germ cells undergo meiosis and cytoplasmic division Cellular descendents of germ cells become gametes Gametes meet at fertilization

4 Asexual Reproduction Single parent produces offspring All offspring are genetically identical to one another and to parent

5 Sexual Reproduction Involves Meiosis Gamete production Fertilization Produces genetic variation among offspring

6 Homologous Chromosomes Carry Different Alleles Cell has two of each chromosome One chromosome in each pair from mother, other from father Pt Paternal and maternal chromosomes carry different alleles

7 Sexual Reproduction Shuffles Alleles Through sexual reproduction, offspring inherit new combinations i of alleles, l which h leads to variations i in traits This variation in traits is the basis for evolutionary change

8 Gamete Formation Gametes are sex cells (sperm, eggs) Arise from germ cells ovaries testes anther ovary Figure 10.2a Page 164

9 Chromosome Number Sum total of chromosomes in a cell Germ cells are diploid (2n) Gametes are haploid (n) Meiosis halves chromosome number

10 Meiosis: Two Divisions Two consecutive nuclear divisions Meiosis I Meiosis II DNA is not duplicated between divisions Four haploid nuclei form

11 Meiosis I Each homologue in the cell pairs with its partner, then the partners separate In-text figure Page 165

12 Meiosis II The two sister chromatids of each duplicated chromosome are separated from each other two chromosomes (unduplicated) one chromosome (duplicated) In-text figure Page 165

13 Meiosis I Stages Prophase I Metaphase I Anaphase I Telophase I Figure 10.4 Page 167

14 Prophase I Each duplicated chromosome pairs with homologue Homologues swap segments Each chromosome becomes attached to spindle Figure 10.4 Page 167

15 Metaphase I Chromosomes are pushed and pulled into the middle of cell The spindle is fully formed Figure 10.4 Page 167

16 Anaphase I Homologous chromosomes segregate The sister chromatids remain attached Figure 10.4 Page 167

17 Telophase I The chromosomes arrive at opposite poles Usually followed by cytoplasmic division Figure 10.4 Page 167

18 Prophase II Microtubules attach to the kinetochores of the duplicated d chromosomes Figure 10.4 Page 167

19 Metaphase II Duplicated chromosomes line up at the spindle equator, midway between the poles Figure 10.4 Page 167

20 Anaphase II Sister chromatids separate to become independent d chromosomes Figure 10.4 Page 167

21 Telophase II The chromosomes arrive at opposite ends of the cell A nuclear envelope forms around each set of chromosomes Four haploid cells Figure 10.4 Page 167

22 Intitial Question: The old fashioned name for meiosis II is reduction division. Why? OBJECTIVES: Compare and contrast Mitosis with Meiosis. STANDARDS: BioB111 Bio.B A4

23 Crossing Over Each chromosome becomes zippered to its homologue All four chromatids are closely aligned Nonsister chromosomes exchange segments Figure 10.5 Page 168

24 Effect of Crossing Over After crossing over, each chromosome contains both maternal and paternal segments Creates new allele combinations in offspring

25 Random Alignment During transition between prophase I and metaphase I, microtubules from spindle poles attach to kinetochores of chromosomes Initial contacts between microtubules and Initial contacts between microtubules and chromosomes are random

26 Random Alignment Either the maternal or paternal member of a homologous pair can end up at either pole The chromosomes in a gamete are a mix of chromosomes from the two parents

27 Possible Chromosome Combinations As a result of random alignment, the number of possible combinations i of chromosomes in a gamete is: 2 n (n is number of chromosome types)

28 Possible Chromosome Combinations or or or Figure 10.6 Page 169

29 Plant Life Cycle mitosis multicelled sporophyte zygote fertilization Diploid Haploid meiosis gametes spores multicelled gametophytes mitosis Figure 10.7 Page 170

30 Animal Life Cycle mitosis zygote multicelled li ll body fertilization Diploid Haploid meiosis gametes Figure 10.7 Page 170

31 Oogenesis first polar body (haploid) three polar bodies (haploid) oogonium primary oocyte (diploid) (diploid) secondary oocyte (haploid) ovum (haploid) Growth Meiosis I, Cytoplasmic Division Meiosis II, Cytoplasmic Division Figure 10.8 Page 171

32 spermatogonium (diploid ) primary spermatocyte (diploid) secondary spermatocytes (haploid) spermatids (haploid) sperm (mature, haploid male gametes) Spermatogenesis Growth Meiosis I, Cytoplasmic Division Meiosis II, Cytoplasmic Division cell differentiation, sperm formation Figure 10.9 Page 171

33 Fertilization Male and female gametes unite and nuclei fuse Fusion of two haploid nuclei produces diploid nucleus in the zygote Which h two gametes unite is random Adds to variation among offspring

34 Factors Contributing to Variation among Offspring Crossing over during prophase I Random alignment of chromosomes at metaphase I Random combination of gametes at fertilization

35 Mitosis & Meiosis Compared Mitosis Functions Asexual reproduction Growth, repair Occurs in somatic cells Produces clones Function Meiosis Sexual reproduction Occurs in germ cells Produces variable offspring

36 Prophase vs. Prophase I Prophase (Mitosis) Homologous pairs do not interact with each other Prophase I (Meiosis) Homologous pairs become zippered together th and crossing over occurs

37 Anaphase, Anaphase I, and Anaphase II Anaphase I (Meiosis) Homologous chromosomes separate from each other Anaphase/Anaphase II (Mitosis/Meiosis) Sister chromatids of a chromosome separate from each other

38 Results of Mitosis and Meiosis Mitosis Two diploid cells produced Each identical to parent Meiosis Four haploid cells produced Differ from parent and one another

39 Closure Cosueactivityty Mitosis Meiosis

40 Intitial Question: Find a partner and take 5 minutes to study for the meiosis quiz. STANDARDS: Bio.B B A B B2 OBJECTIVES: Students will utilize the study guide to review for the Mitosis/Meiosis test. Below are the objectives for the test: Explain the role of mitosis in the formation of new cells and its importance in maintaining chromosome number during asexual reproduction Summarize the stages of the cell cycle. Describe the events that occur during meiosis Based on the steps of meiosis, conclude why meiosis leads to genetic diversityi Label and describe the events that occur during Meiosis. Compare Mitosis with Meiosis.

41 Ticket Out the Door The generalized life cycle of complex land plants is often described as alternation of generations. Describe the meaning of this phrase.

42 Intitial Question: Find a partner and take 5 minutes to study for the mitosis/meiosis test STANDARDS: Bio.B A B B2 OBJECTIVES: Students will utilize the study guide to review for the Mitosis/Meiosis test. Below are the objectives for the test: Explain the role of mitosis in the formation of new cells and its importance in maintaining chromosome number during asexual reproduction Summarize the stages of the cell cycle. Describe the events that occur during meiosis Based on the steps of meiosis, conclude why meiosis leads to genetic diversityi Label and describe the events that occur during Meiosis. Compare Mitosis with Meiosis.

Meiosis and Sexual Reproduction

Meiosis and Sexual Reproduction Asexual Reproduction Single parent produces offspring All offspring are genetically identical to one another and to parent Produces identical somatic (body) cells Sexual