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Chapter 8: Cell Reproduction

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Title: Chapter 8: Cell Reproduction


1
Chapter 8 Cell Reproduction
0
Original slide set from www.laney.edu/wp/laura_co
ronado/files/2011/08/SVChap-8.ppt
2
STANDARDS
  • SPI 3210.1.6 - Describe the relationship between
    the cell cycle and reproduction.
  • - I can determine the movement of
    chromosomes during cell reproduction.

3
With your partner
  • Find two different definitions of chromosome

4
Chromosome Structure
  • Chromosome definition

in a eukaryotic cell, one of the structures in
the nucleus that are made up of DNA and protein
in a prokaryotic cell, the main ring of DNA
5
Chromosomes
  • What do they look like?
  • How many do humans have?

They look like an X just before the cell
divides and an I after they divide.
46 chromosomes (23 from mom, 23 from dad)
6
With your partner
  • Explain the difference in the two shapes of
    chromosomes

7
Chromosome Vocabulary
  • Histones
  • Chromatid
  • Centromere

a type of protein found in the chromosomes of
eukaryotic cells but not prokaryotic cells.
one side of a chromosome that become visible
during meiosis or mitosis
The region of the chromosome that holds the two
sister chromatids together during mitosis
8
Chromosome or Chromatin?
  • Chromosome
  • Chromatin

Tightly coiled DNA proteins during cell
division DNA cannot be read while in this form.
Loosely coiled DNA proteins during the cells
life other than cell division. DNA can be read
to direct activities of the cell.
9
(No Transcript)
10
WITH YOUR PARTNER
  • Do more complex organisms have more chromosomes?

11
What is cell reproduction?
12
WHAT CELL REPRODUCTION ACCOMPLISHES
  • Reproduction
  • May result in the birth of new organisms
  • More commonly involves the production of new
    cells

13
Cell Division
  • Cell division plays important roles in the lives
    of organisms.
  • Replaces damaged or lost cells
  • Permits growth
  • Allows for reproduction

14
FUNCTIONS OF CELL DIVISION
Cell Replacement
Growth via Cell Division
Colorized TEM
LM
Human kidney cell
Early human embryo
Figure 8.1a
15
Asexual Reproduction
  • Single-celled organisms reproduce by simple cell
    division
  • There is no fertilization of an egg by a sperm
  • The parent and its offspring have identical
    genes.

16
Asexual Reproduction
  • Binary Fission
  • Prokaryotic cells divide through a simple form of
    division called Binary Fission
  • 3 step process
  • Single naked strand splits and forms a
    duplicate of itself.
  • The two copies move to opposite sides of the cell
  • Cell pinches into two new and identical cells
    called "daughter cells". (Cell wall then forms if
    applicable)

17
Asexual Reproduction
  • Mitosis is the type of cell division responsible
    for
  • Asexual reproduction
  • Growth and maintenance of multicellular organisms
  • Some multicellular organisms, such as sea stars,
    can grow new individuals from fragmented pieces.
  • Growing a new plant from a clipping

18
FUNCTIONS OF CELL DIVISION
Asexual Reproduction
LM
Sea stars
African Violet
Amoeba
Figure 8.1b
19
Sexual Reproduction
  • Sexual reproduction requires fertilization of an
    egg by a sperm using a special type of cell
    division called meiosis.
  • Thus, sexually reproducing organisms use
  • Meiosis for reproduction
  • Mitosis for growth and maintenance

20
LM
Chromosomes
Figure 8.3
21
Chromosomes
  • Chromosomes
  • Are made of chromatin, a combination of DNA and
    protein molecules
  • Are not visible in a cell until cell division
    occurs
  • Before a parent cell splits into two, it
    duplicates its chromosomes

22
Number of chromosomes in body cells
Species
Indian muntjac deer
6
Koala
16
Opossum
22
Giraffe
30
40
Mouse
Human
46
Duck-billed platypus
54
60
Buffalo
Dog
78
102
Red viscacha rat
Figure 8.2
23
Eukaryotic Cell Genetic Information
  • Most genes on chromosomes in cell nucleus
  • A few genes found in mitochondrial and
    chloroplast DNA
  • Each chromosome one very long DNA molecule,
    typically with thousands of genes.
  • Histones are proteins used to package DNA.
  • Nucleosomes consist of DNA wound around histone
    molecules.

24
DNA double helix
Histones
Beads on a string
TEM
Nucleosome
Tight helical fiber
Looped domains
Duplicated chromosomes (sister chromatids)
TEM
Centromere
Figure 8.4
25
Chromosome (one long piece of DNA)
Centromere
Sister chromatids
Duplicated chromosome
Figure 8.UN2
26
Chromosomes
  • Before a cell divides, it duplicates all of its
    chromosomes, resulting in two copies called
    sister chromatids.
  • Sister chromatids are joined together at a narrow
    waist called the centromere.
  • When the cell divides, the sister chromatids
    separate from each other.
  • Once separated, each chromatid is
  • Considered a full-fledged chromosome
  • Identical to the original chromosome

27
Chromosome duplication
Sister chromatids
Figure 8.5
28
The Cell Cycle
  • A cell cycle is the orderly sequence of events
    that extend from the time a cell is first formed
    from a dividing parent cell to its own division
    into two cells.
  • The cell cycle consists of two distinct phases
  • Interphase
  • The mitotic phase

29
S phase (DNA synthesis chromosome duplication)
Interphase metabolism and growth (90 of time)
G1
G2
Mitotic (M) phase cell division (10 of time)
Cytokinesis (division of cytoplasm)
Mitosis (division of nucleus)
Figure 8.6
30
Interphase
31
Interphase
  • Most of a cell cycle is spent in interphase.
  • During interphase, a cell
  • Performs its normal functions
  • Doubles everything in its cytoplasm
  • Grows in size

32
Interphase
  • Interphase
  • 3 Stages
  • G1 (Gap 1) Phase - Cell performs its normal
    function (cells which do not divide stay in this
    stage for their entire life span)
  • -cells grow and mature
  • S (Synthesis) Phase - Here the cell actively
    duplicates its DNA in preparation for division
  • G2 (Gap 2) Phase - Amount of cytoplasm (including
    organelles) increases in preparation for
    division.
  • Another possibility
  • G0 Phase cells do not prepare for cell division
  • Generally straight from G1 phase
  • Example fully developed cells in Central Nervous
    System never divide again

33
Mitosis
34
Mitosis
  • The mitotic (M) phase includes two overlapping
    processes
  • Mitosis, in which the nucleus and its contents
    divide evenly into two daughter nuclei
  • Cytokinesis, in which the cytoplasm is divided in
    two

35
Mitosis and Cytokinesis
  • Mitosis consists of four distinct phases
  • (A) Prophase
  • (B) Metaphase
  • (C) Anaphase
  • (D) Telophase
  • Cytokinesis typically
  • Occurs during telophase
  • Divides the cytoplasm
  • Is different in plant and animal cells

36
PROPHASE
INTERPHASE
Fragments of nuclear envelope
Early mitotic spindle
Centrosomes (with centriole pairs)
Centrosome
Chromatin
Centromere
Nuclear envelope
Chromosome, consisting of two sister chromatids
Spindle microtubules
Plasma membrane
LM
Figure 8.7.a
37
Prophase
  • Chromosomes condense
  • Nuclear membrane breaks down
  • Centrioles migrate to opposite poles (in animal
    cells)
  • Microtubules attach to chromosomes and centrioles

38
Prophase
39
ANAPHASE
METAPHASE
TELOPHASE AND CYTOKINESIS
Cleavage furrow
Nuclear envelope forming
Spindle
Daughter chromosomes
Figure 8.7b
40
Metaphase
  • Chromosomes line up along the center of the cell

41
Metaphase
42
Anaphase
  • Microtubules shorten
  • Chromatids separate a pull to opposite sides

43
Anaphase
44
Telophase
  • Nuclear membrane forms around each set of
    chromosomes
  • Chromosomes unwind

45
Cytokinesis
  • Cytoplasm split in two
  • Cell membrane separates the two daughter cells

46
Telophase and Cytokinesis
47
Animal cell mitosis
48
SEM
Cleavage furrow
Cleavage furrow
Contracting ring of microfilaments
Daughter cells
Figure 8.8a
49
Plant Cell Mitosis
  • Plant cell mitosis is similar to animal cell
    mitosis BUT cytokinesis is different
  • In plant, fungi and algae cell, a cell plate
    forms in the middle of the cell to divide the two
    cells.

50
Wall of parent cell
Cell plate forming
Daughter nucleus
LM
Vesicles containing cell wall material
New cell wall
Cell plate
Cell wall
Daughter cells
Figure 8.8b
51
Result of Mitosis
  • 2 daughter cells that are identical to each other
    and identical to the parent cell

52
Cancer Cells Growing Out of Control
  • Normal plant and animal cells have a cell cycle
    control system that consists of specialized
    proteins, which send stop and go-ahead
    signals at certain key points during the cell
    cycle.

53
What Is Cancer?
  • Cancer is a disease of the cell cycle.
  • Cancer cells do not respond normally to the cell
    cycle control system.
  • Cancer cells can form tumors, abnormally growing
    masses of body cells.
  • The spread of cancer cells beyond their original
    site of origin is metastasis.
  • Malignant tumors can
  • Spread to other parts of the body
  • Interrupt normal body functions

54
Lymph vessels
Tumor
Blood vessel
Glandular tissue
A tumor grows from a single cancer cell.
Cancer cells invade neighboring tissue.
Metastasis Cancer cells spread through lymph and
blood vessels to other parts of the body.
Figure 8.9
55
Cancer Treatment
  • Cancer treatment can involve
  • Radiation therapy, which damages DNA and disrupts
    cell division
  • Chemotherapy, which uses drugs that disrupt cell
    division

56
Cancer Prevention and Survival
  • Certain behaviors can decrease the risk of
    cancer
  • Not smoking
  • Exercising adequately
  • Avoiding exposure to the sun
  • Eating a high-fiber, low-fat diet
  • Performing self-exams
  • Regularly visiting a doctor to identify tumors
    early

57
Meiosis
58
Homologous Chromosomes
  • Different individuals of a single species have
    the same number and types of chromosomes.
  • A human somatic cell
  • Is a typical body cell
  • Has 46 chromosomes
  • A karyotype is an image that reveals an orderly
    arrangement of chromosomes.
  • Homologous chromosomes are matching pairs of
    chromosomes that can possess different versions
    of the same genes.

59
LM
Pair of homologous chromosomes
Centromere
Sister chromatids
One duplicated chromosome
Figure 8.11
60
Human Chromosomes
  • Humans have
  • Two different sex chromosomes, X and Y
  • Twenty-two pairs of matching chromosomes, called
    autosomes
  • Humans are diploid organisms in which
  • Their somatic cells contain two sets of
    chromosomes
  • Their gametes are haploid, having only one set of
    chromosomes

61
Gametes and the Life Cycle of a Sexual Organism
  • The life cycle of a multicellular organism is the
    sequence of stages leading from the adults of one
    generation to the adults of the next.

62
Haploid gametes (n ? 23)
Egg cell
n
n
Sperm cell
MEIOSIS
FERTILIZATION
Multicellular diploid adults (2n ? 46)
Diploid zygote (2n ? 46)
2n
MITOSIS
and development
Key
Haploid (n)
Diploid (2n)
Figure 8.12
63
Meiosis
  • Humans are diploid organisms in which
  • Their somatic cells contain two sets of
    chromosomes
  • Their gametes are haploid, having only one set of
    chromosomes
  • In humans, a haploid sperm fuses with a haploid
    egg during fertilization to form a diploid
    zygote.
  • Sexual life cycles involve an alternation of
    diploid and haploid stages.
  • Meiosis produces haploid gametes, which keeps the
    chromosome number from doubling every generation.

64
Homologous chromosomes separate.
Chromosomes duplicate.
Sister chromatids separate.
Duplicated pair of homologous chromosomes
Pair of homologous chromosomes in diploid parent
cell
Sister chromatids
MEIOSIS I
MEIOSIS II
INTERPHASE BEFORE MEIOSIS
Figure 8.13-3
65
The Process of Meiosis
  • In meiosis
  • Haploid daughter cells are produced in diploid
    organisms
  • Interphase is followed by two consecutive
    divisions, meiosis I and meiosis II
  • Crossing over occurs

66
MEIOSIS I HOMOLOGOUS CHROMOSOMES SEPARATE
INTERPHASE
PROPHASE I
METAPHASE I
ANAPHASE I
Sister chromatids remain attached
Microtubules attached to chromosome
Sites of crossing over
Centrosomes (with centriole pairs)
Spindle
Sister chromatids
Nuclear envelope
Centromere
Pair of homologous chromosomes
Chromatin
Homologous chromosomes pair up and exchange segmen
ts.
Pairs of homologous chromosomes split up.
Pairs of homologous chromosomes line up.
Chromosomes duplicate.
Figure 8.14a
67
MEIOSIS II SISTER CHROMATIDS SEPARATE
TELOPHASE II AND CYTOKINESIS
ANAPHASE II
TELOPHASE I AND CYTOKINESIS
PROPHASE II
METAPHASE II
Cleavage furrow
Sister chromatids separate
Haploid daughter cells forming
Two haploid cells form chromosomes are
still doubled.
During another round of cell division, the
sister chromatids finally separate four
haploid daughter cells result, containing
single chromosomes.
Figure 8.14b
68
LM
Figure 8.14bc
69
Review Comparing Mitosis and Meiosis
  • In mitosis and meiosis, the chromosomes duplicate
    only once, during the preceding interphase.
  • The number of cell divisions varies
  • Mitosis uses one division and produces two
    diploid cells
  • Meiosis uses two divisions and produces four
    haploid cells
  • All the events unique to meiosis occur during
    meiosis I, while meiosis II is the same as
    mitosis since it separates sister chromatids.

70
MITOSIS
MEIOSIS
Prophase I
Prophase
MEIOSIS I
Chromosome duplication
Chromosome duplication
Duplicated chromosome (two sister chromatids)
Parent cell (before chromosome duplication) 2n ?
4
Homologous chromosomes come together in pairs.
Site of crossing over between homologous (nonsiste
r) chromatids
Metaphase
Metaphase I
Chromosomes align at the middle of the cell.
Homologous pairs align at the middle of the
cell.
Anaphase Telophase
Anaphase I Telophase I
Chromosome with two sister chromatids
Sister chromatids separate during anaphase.
Homologous chromosomes separate during anaphase
I sister chromatids remain together.
Haploid n ? 2
Daughter cells of meiosis I
2n
2n
MEIOSIS II
Daughter cells of mitosis
Sister chromatids separate during anaphase II.
n
n
n
n
Daughter cells of meiosis II
Figure 8.15
71
Independent Assortment of Chromosomes
  • When aligned during metaphase I of meiosis, the
    side-by-side orientation of each homologous pair
    of chromosomes is a matter of chance.
  • Every chromosome pair orients independently of
    the others during meiosis.
  • For any species the total number of chromosome
    combinations that can appear in the gametes due
    to independent assortment is
  • 2n where n is the haploid number.
  • For a human
  • n 23
  • 223 8,388,608 different chromosome combinations
    possible in a gamete

72
POSSIBILITY 2
POSSIBILITY 1
Metaphase of meiosis I
Metaphase of meiosis II
Gametes
Combination a
Combination b
Combination c
Combination d
Figure 8.16-3
73
Random Fertilization
  • A human egg cell is fertilized randomly by one
    sperm, leading to genetic variety in the zygote.
  • If each gamete represents one of 8,388,608
    different chromosome combinations, at
    fertilization, humans would have 8,388,608
    8,388,608, or more than 70 trillion, different
    possible chromosome combinations.

74
Figure 8.17
75
Crossing Over
  • In crossing over
  • Homologous chromosomes exchange genetic
    information
  • Genetic recombination, the production of gene
    combinations different from those carried by
    parental chromosomes, occurs

76
Prophase I of meiosis
Duplicated pair of homologous chromosomes
Homologous chromatids exchange corresponding segme
nts.
Chiasma, site of crossing over
Metaphase I
Spindle microtubule
Sister chromatids remain joined at
their centromeres.
Metaphase II
Gametes
Recombinant chromosomes combine
genetic information from different parents.
Recombinant chromosomes
Figure 8.18-5
77
How Accidents during Meiosis Can Alter Chromosome
Number
  • In nondisjunction, the members of a chromosome
    pair fail to separate during anaphase, producing
    gametes with an incorrect number of chromosomes.
  • Nondisjunction can occur during meiosis I or II.
  • If nondisjunction occurs, and a normal sperm
    fertilizes an egg with an extra chromosome, the
    result is a zygote with a total of 2n 1
    chromosomes.
  • If the organism survives, it will have an
    abnormal number of genes.

78
NONDISJUNCTION IN MEIOSIS II
NONDISJUNCTION IN MEIOSIS I
Meiosis I
Nondisjunction Pair of homologous chromosomes
fails to separate.
Meiosis II
Nondisjunction Pair of sister chromatids fails
to separate.
Gametes
Number of chromosomes
n
n 1
n 1
n 1
n
n ? 1
n ? 1
n ? 1
Abnormal gametes
Abnormal gametes
Normal gametes
Figure 8.20-3
79
Abnormal egg cell with extra chromosome
n ? 1
Normal sperm cell
Abnormal zygote with extra chromosome 2n ? 1
n (normal)
Figure 8.21
80
Down Syndrome
  • Down Syndrome
  • Is also called trisomy 21
  • Is a condition in which an individual has an
    extra chromosome 21
  • Affects about one out of every 700 children
  • The incidence of Down Syndrome increases with the
    age of the mother.

81
LM
Chromosome 21
Figure 8.22
82
90
80
70
60
Infants with Down syndrome (per 1,000 births)
50
40
30
20
10
0
25
35
45
20
30
40
50
Age of mother
Figure 8.23
83
Abnormal Numbers of Sex Chromosomes
  • Nondisjunction can also affect the sex
    chromosomes.

84
Table 8.1
85
Evolution Connection The Advantages of Sex
  • Asexual reproduction conveys an evolutionary
    advantage when plants are
  • Sparsely distributed
  • Superbly suited to a stable environment
  • Sexual reproduction may convey an evolutionary
    advantage by
  • Speeding adaptation to a changing environment
  • Allowing a population to more easily rid itself
    of harmful genes

86
Figure 8.24
87
Distribution via mitosis
Duplication of all chromosomes
Genetically identical daughter cells
Figure 8.UN1
88
S phase DNA synthesis chromosome duplication
Interphase Cell growth and chromosome duplication
G2
G1
Mitotic (M) phase
Genetically identical daughter cells
Cytokinesis (division of cytoplasm)
Mitosis (division of nucleus)
Figure 8.UN3
89
Human Life Cycle
Haploid gametes (n ? 23)
Key
n
Haploid (n)
Egg cell
Diploid (2n)
n
Sperm cell
MEIOSIS
FERTILIZATION
Diploid zygote (2n ? 46)
Male and female diploid adults (2n ? 46)
2n
MITOSIS
and development
Figure 8.UN4
90
MITOSIS
MEIOSIS
Parent cell (2n)
Parent cell (2n)
MEIOSIS I
Chromosome duplication
Pairing of homologous chromosome
Chromosome duplication
Crossing over
Daughter cells
2n
2n
MEIOSIS II
n
n
n
n
Daughter cells
Figure 8.UN5
91
Differences between Mitosis and Meiosis
  • Meiosis has 2 divisions two rounds of
    chromosome separation.
  • Crossing over in meiosis exchange of genetic
    material between homologous chromosomes occurs
    during synapsis(pairing of homologous chromosomes
    in M I)

92
Differences between Mitosis and Meiosis
  • Mitosis occurs in all cells, meiosis limited to
    certain cells
  • Mitosis produces 2 identical cells, Meiosis
    produce 4 cells which are not identical
  • Mitosis daughter cells of same ploidy as
    parent Meiosis daughter cells haploid of parent

93
LM
(b)
(a)
(c)
(d)
Figure 8.UN6
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