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Chapter 10

Chapter 10. Meiosis and Sexual Reproduction. Bozeman Video—Cell Cycle, Mitosis, & Meiosis. http:// www.youtube.com/watch?v=2aVnN4RePyI. Impacts, Issues: Why Sex. Asexual reproduction is easier and faster Sexual reproduction can be an alternative adaption in changing environments.

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Chapter 10

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  1. Chapter 10 Meiosis and Sexual Reproduction

  2. Bozeman Video—Cell Cycle, Mitosis, & Meiosis http://www.youtube.com/watch?v=2aVnN4RePyI

  3. Impacts, Issues: Why Sex • Asexual reproduction is easier and faster • Sexual reproduction can be an alternative adaption in changing environments

  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. SOMATIC VS GAMETE CELLS

  7. AUTOSOMES VS. SEX CHROMOSOMES

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

  9. Homologous Chromosomes Fig. 10-2, p.156

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

  11. Gamete Formation • Gametes are sex cells (sperm, eggs) • Arise from germ cells ovaries anther ovary testes Figure 10-3Page 156

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

  13. Human Karyotype 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 XX (or XY) Fig. 10-4, p.157

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

  15. Meiosis I Each homologue in the cell pairs with its partner, then the partners separate p. 158

  16. Meiosis II • The two sister chromatids of each duplicated chromosome are separated from each other two chromosomes (unduplicated) one chromosome (duplicated) p. 158

  17. Prophase I Metaphase I Anaphase I Telophase I Meiosis I - Stages

  18. Prophase I • Each duplicated chromosome pairs with homologue • Homologues swap segments(THIS IS KNOWN AS CROSSING OVER WHICH OCCURS AT A SITE CALLED THE CHIASMATA) • Each chromosome becomes attached to spindle • Longest phase of meiosis Fig. 10-5, p. 158

  19. Metaphase I • Tetrads are aligned on the metaphase plate • Chromosomes are pushed and pulled into the middle of cell • The spindle is fully formed Fig. 10-5, p. 158

  20. Anaphase I • Homologous chromosomes segregate to opposite poles • The sister chromatids remain attached Fig. 10-5, p. 158

  21. Telophase I • The chromosomes arrive at opposite poles • Usually followed by cytoplasmicdivision • Interkinesis (reforming of the nuclear membrane)may occur before Meiosis II but no more DNA duplication Fig. 10-5, p. 158

  22. Prophase II • Microtubules attach to the kinetochores of the duplicated chromosomes • If interkinesis happened, the nuclear membrane redisappears Fig. 10-5, p. 158

  23. Metaphase II • Duplicated chromosomes line up singly at the spindle equator, midway between the poles Fig. 10-5, p. 158

  24. Anaphase II • Sister chromatids and their centromeresseparate to become independent chromosomes at opposite poles of each cell Fig. 10-5, p. 158

  25. TelophaseII and Cytokinesis • The chromosomes have arrived at opposite ends of the cell • A nuclear envelope forms around each set of chromosomes • Four haploid cells Fig. 10-5, p. 158

  26. newly forming microtubules spindle equator one pair of homologous chromosomes Prophase I Metaphase I Anaphase I Telophase I Meiosis I Stepped Art Fig. 10-5a, p.158

  27. Prophase II Metaphase II Anaphase II Telophase II Meiosis II Stepped Art Fig. 10-5b, p.159

  28. Crossing Over • Each chromosome becomes zippered to its homologue • All four chromatids are closely aligned • Nonsister chromosomes exchange segments

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

  30. 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

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

  32. Bozeman Video--Meiosis http://www.youtube.com/watch?v=rB_8dTuh73c

  33. ROLES OF MITOSIS/MEIOSIS IN LIFE CYCLES

  34. Plant Life Cycle sporophyte zygote diploid fertilization meiosis haploid spores gametes gametophytes Fig. 10-8a, p.162

  35. Animal Life Cycle multicelled body zygote diploid fertilization meiosis haploid gametes Fig. 10-8b, p.162

  36. FUNGAL AND ALGAL LIFE CYCLE

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

  38. Factors Contributing to Variation among Offspring • Crossing over during prophase I • Random alignment of chromosomes at metaphase I (AKA Law of Independent Assortment of Chromosomes) • Random combination of gametes at fertilization (1 in 8 million possible egg combinations x 1 in 8 million posssible sperm combinations = 1 in 64 trillion possible zygote • Natural Selection-increases frequency of reproductively favorable traits

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

  40. Bozeman –Mitosis/Meiosis Bead Simulation http://www.youtube.com/watch?v=zGVBAHAsjJM&feature=c4-overview&playnext=1&list=TLZldufdv0wDU

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

  42. 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

  43. Comparison of Mitosis and Meiosis

  44. Meiosis Square Dance Video http://www.youtube.com/watch?v=eaf4j19_3Zg

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