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Meiosis and Sexual Life Cycles

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Meiosis and Sexual Life Cycles

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    1. Meiosis and Sexual Life Cycles Chapter 13 A. P. Biology Mr. Knowles Liberty Senior High School

    2. Mitosis- Review

    3. Mutations

    4. Comparison of Asexual and Sexual Reproduction In asexual reproduction One parent produces genetically identical offspring by mitosis

    5. In sexual reproduction: Two parents give rise to offspring that have unique combinations of genes inherited from the two parents.

    6. Leewenhoeks Early Ideas of Sperm

    8. Somatic (nonreproductive cells) are diploid. Body cells. Human somatic cells have 46 chromosomes. Gametes (reproductive cells) are haploid. Human sperm and ova have 23 chromosomes. Types of Cells

    9. Gametes Fuse to Form a Zygote

    10. During fertilization: These gametes, sperm and ovum, fuse, forming a diploid zygote. The zygote Develops into an adult organism.

    11. Fertilization or Syngamy

    14. Zygote Undergoes Mitosis

    15. Zygote is Diploid (2n)

    16. Why is the number of chromosomes in gametes that of somatic cells? If not, after 10 generations the 46 chromosomes in human cells would increase to over 46 X 210.

    17. Meiosis A process of cell division in which the number of chromosomes in certain cells is halved during gamete formation. A reduction division.

    19. The Human Life Cycle

    20. The Variety of Sexual Life Cycles The three main types of sexual life cycles: Differ in the timing of meiosis and fertilization

    21. In animals Meiosis occurs during gamete formation Gametes are the only haploid cells

    22. Plants and some algae: Exhibit an alternation of generations. The life cycle includes both diploid and haploid multicellular stages.

    24. In most fungi and some protists: Meiosis produces haploid cells that give rise to a haploid multicellular adult organism The haploid adult carries out mitosis, producing cells that will become gametes

    25. Sexual Life Cycle Reproduction that alternates between fertilization (a diploid state) and meiosis (a haploid state) sexual reproduction. Sexual reproduction provides DNA from both parents.

    26. Some Sexual Life Cycles Unicellular Protists individual cells function as gametes?undergo meiosis and fuse with others. Plants- may produce haploid cells ?undergo mitosis and produce a multicellular haploid organism. Animals- set aside germ cells? undergo meiosis and become haploid gametes.

    27. The Stages of Meiosis An overview of meiosis

    28. Interphase and Meiosis I

    29. Telophase I, Cytokinesis, and Meiosis II

    30. Meiosis Two nuclear divisions. Labeled PMAT I and PMAT II. Prophase I is very different in meiosis than in mitosis.

    31. Interphase I

    33. Prophase I

    34. Synapsis in Prophase I

    35. Prophase I The duplicated homologous chromosomes condense and the ends of chromatids attach to the nuclear envelope. Homologous pairs align next to each other. The chromatids of one homologue align in precise register with the chromatids of the other in a process called synapsis (zipping up a zipper).

    36. Prophase I The DNA of chromatids unwind and base pair with the complementary strand on the the other homologue. The crossed-over sister chromatids form an X-shaped structure chiasma. DNA from one homologue sister chromatid is exchanged with the other Crossing Over.

    37. Crossing Over During Prophase I

    38. Prophase I The chiasmata hold the two pairs of sister chromatids together at the ends Terminal Chiasmata. The homologous chromatids have exchanged DNA.

    39. Prophase I

    40. Metaphase I

    41. Metaphase I Terminal chiasmata are still formed. The nuclear membrane breaks down and spindle fibers are forming. Only one side of each centromere faces outward toward the growing spindle fiber. The fibers can attach to kinetochore proteins on only one side of each centromere.

    42. Metaphase I Alignment of each pair on the metaphase plate is random. Either homologue may be situated toward a given pole.

    43. Metaphase I

    44. Anaphase I

    45. Anaphase I Spindle fibers contract and break the chiasmata and pull the centromeres toward the poles. The entire centromere of the homologue proceeds to one pole. (Different than mitosis). Each pole receives a haploid number of chromosomes, one member of each homologous pair.

    46. Anaphase I

    47. Anaphase I Because the orientation of the homologous chromosomes on the metaphase plate is random, genes on separate chromosomes are inherited independently Independent Assortment.

    48. Telophase 1

    49. Telophase I Individual chromosomes cluster at the poles. Each chromosome is made of two chromatids that are not identical because of crossing over that occurred in Prophase I. Cytokinesis may or may not occur after Telophase I. Nuclei may not reform.

    50. Telophase I

    51. The Second Meiotic Division No DNA replication before this division (Different than mitosis). Undergo a simple mitotic division with the products from Telophase I. Results are four haploid cells. Nuclei are reorganized.

    53. Prophase II

    54. Metaphase II

    55. Metaphase II

    56. Anaphase II

    57. Anaphase II

    58. Telophase II

    59. Telophase II

    64. Comparison of Mitosis and Meiosis

    65. A Comparison of Mitosis and Meiosis Meiosis and mitosis can be distinguished from mitosis by three events in Meiosis l: Synapsis and crossing over- Homologous chromosomes physically connect and exchange genetic information. Tetrads on the metaphase plate- At metaphase I of meiosis, paired homologous chromosomes (tetrads) are positioned on the metaphase plates Separation of homologues: At anaphase I of meiosis, homologous pairs move toward opposite poles of the cell In anaphase II of meiosis, the sister chromatids separate

    66. Concept 13.4: Genetic variation produced in sexual life cycles contributes to evolution 3 Sources of Genetic Variation: 1. Reshuffling of genetic material in meiosis-Crossing Over. 2. Homologous pairs of chromosomes are oriented randomly at metaphase - Independent Assortment. 3. Random Fertilization of Gametes- Will produce a zygote with any of about 64 trillion diploid combinations

    67. Crossing Over Crossing over: Produces recombinant chromosomes that carry genes derived from two different parents

    68. Independent Assortment Each pair of chromosomes sorts its maternal and paternal homologues into daughter cells independently of the other pairs

    69. Evolutionary Significance of Genetic Variation Within Populations Genetic variation: -Is the raw material for evolution by natural selection Mutations: Are the original source of genetic variation Sexual reproduction: Produces new combinations of variant genes, adding more genetic diversity

    70. The Fate of Haploid Cells

    71. Gametogenesis Meiotic divisions that result in gametes.

    78. Fertilization or Syngamy

    79. Zygote is Diploid (2n)

    81. Cloning to Save an Endangered Species

    82. Microtubules and Motor Proteins-Spindle Fibers

    83. Cloned Animals as of 4-04

    84. What animal group hasnt been clonedyet?

    86. Can haploid cells develop into functioning animals or plants?

    87. How to make a bee colony?

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