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Meiosis and Sexual Life Cycles

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Meiosis and Sexual Life Cycles Chapter 13 A. P. Biology Mr. Knowles Liberty Senior High School Mitosis- Review Mutations Comparison of Asexual and Sexual Reproduction ... – PowerPoint PPT presentation

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Title: Meiosis and Sexual Life Cycles


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
7
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8
Types of Cells
  • 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.

9
Gametes Fuse to Form a Zygote
n
2n
Syngamy
n
10
  • During fertilization
  • These gametes, sperm and ovum, fuse, forming a
    diploid zygote.
  • The zygote
  • Develops into an adult organism.

11
Fertilization or Syngamy
12
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13
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14
Zygote Undergoes Mitosis
15
Zygote is Diploid (2n)
16
Why is the number of chromosomes in gametes ½
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.

18
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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.

23
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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

Figure 13.8
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
32
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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.

52
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53
Prophase II
54
Metaphase II
55
Metaphase II
56
Anaphase II
57
Anaphase II
58
Telophase II
59
Telophase II
60
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61
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62
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63
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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

Figure 13.10
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
n
Undergo Mitosis? Multicellular
Gametes
sperm
ova
n
n
Haploid Plants
Haploid Fungi
71
Gametogenesis
  • Meiotic divisions that result in gametes.

72
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73
Oogenesis Spermatogenesis
Oogonium (female germ cell, 2n)
Spermatogonium (male germ cell, 2n)
Germ cells committed to meiosis
Primary Oocyte (2n)
Primary Spermatocyte (2n)
First Meiotic Division
___Before Ovulation____
Secondary Spermatocyte (n)
Secondary Spermatocyte (n)
Secondary Ooctye (n)
First Polar Body (n)
Second Meiotic Division
___After Fertilization____
Four Spermatids (n)
Second Polar Body (n)
Ovum (n)
Four Spermatozoa (n)
74
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75
Primary Spermatocytes
Seminiferous Tubule
Spermatids
Mature Sperm
76
Rat Sperm
77
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78
Fertilization or Syngamy
79
Zygote is Diploid (2n)
80
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81
Cloning to Save an Endangered Species
Enculeated Cow Egg
Bateng Nucleus
Surrogate Cow
Frozen Bateng Cells
Cloned Bateng
82
Microtubules and Motor Proteins-Spindle Fibers
83
Cloned Animals as of 4-04
84
What animal group hasnt been clonedyet?
Primates Why?
85
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86
Can haploid cells develop into functioning
animals or plants?
Bees Do It!
87
How to make a bee colony?
Fertilized Egg, (2n)
Female Worker, (2n)
Meiosis
Mitosis w/o Cytokinesis
Unfertilized Egg, (1n)
Queen, (2n)
Male Drone, (1n)
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