Download MEIOSIS I

CAMPBELL BIOLOGY IN FOCUS
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
10
Meiosis and
Sexual Life Cycles
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
© 2014 Pearson Education, Inc.
Inheritance of Genes
 Each gene has a specific locus, on a certain
chromosome
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Sets of Chromosomes in Human Cells
 A karyotype is an ordered display of the pairs of
chromosomes from a cell
 The 2 in each pair are called homologous
chromosomes, or homologs
 These carry genes controlling the same inherited
characters – 1 from each parent
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Figure 10.3
Application
Technique
Pair of homologous
duplicated chromosomes
Centromere
Sister
chromatids
Metaphase
chromosome
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5 m
 The sex chromosomes are called X and Y
 remaining 22 pairs are called autosomes
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Figure 10.4
Key
2n  6
Maternal set of
chromosomes (n  3)
Paternal set of
chromosomes (n  3)
Sister chromatids
of one duplicated
chromosome
Two nonsister
chromatids in
a homologous pair
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Centromere
Pair of homologous
chromosomes
(one from each set)
Animal Life Cycle
multicelled
body
zygote
fertilization
diploid
haploid
meiosis
gametes
© 2014 Pearson Education, Inc.
Fig. 10-8b, p.162
Figure 10.6a
Key
n
Gametes
n
n
MEIOSIS
2n
Diploid
multicellular
organism
(a) Animals
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FERTILIZATION
Zygote
2n
Mitosis
Haploid (n)
Diploid (2n)
Figure 10.6b
Haploid multicellular organism
(gametophyte)
Mitosis
n
Key
Haploid (n)
Diploid (2n)
Mitosis
n
n
Spores
MEIOSIS
2n
Diploid
multicellular
organism
(sporophyte)
Gametes
FERTILIZATION
2n
Mitosis
(b) Plants and some algae
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n
n
Zygote
Figure 10.6c
Haploid unicellular or
multicellular organism
Mitosis
Key
Haploid (n)
Diploid (2n)
Mitosis
n
n
n
n
Gametes
FERTILIZATION
MEIOSIS
2n
Zygote
(c) Most fungi and some protists
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n
Concept 10.3: Meiosis reduces the number of
chromosome sets from diploid to haploid
 Meiosis 2 sets of cell divisions…meiosis I and
meiosis II
 results in 4 haploid daughter cells (that become
gametes)
© 2014 Pearson Education, Inc.
Figure 10.7
Interphase
Pair of homologous
chromosomes in
diploid parent cell
Chromosomes
duplicate
Duplicated pair
of homologous
chromosomes
Sister
chromatids
Diploid cell with
duplicated
chromosomes
Meiosis I
1 Homologous
chromosomes
separate
Meiosis II
Haploid cells with
duplicated chromosomes
2 Sister chromatids
separate
Haploid cells with unduplicated chromosomes
© 2014 Pearson Education, Inc.
Figure 10.7a
Interphase
Pair of homologous
chromosomes in
diploid parent cell
Duplicated pair
of homologous
chromosomes
Sister
chromatids
© 2014 Pearson Education, Inc.
Chromosomes
duplicate
Diploid cell with
duplicated
chromosomes
Figure 10.7b
Meiosis I
1 Homologous
chromosomes
separate
Meiosis II
Haploid cells with
duplicated chromosomes
2 Sister chromatids
separate
Haploid cells with unduplicated chromosomes
© 2014 Pearson Education, Inc.
 Meiosis I, homologous pairs pair and separate
 Meiosis II, sister chromatids separate
Animation: Meiosis
Video: Meiosis I in Sperm Formation
© 2014 Pearson Education, Inc.
Figure 10.8a
MEIOSIS I: Separates homologous chromosomes
Prophase I
Metaphase I
Anaphase I
Telophase I and
Cytokinesis
Sister
chromatids
Centromere
(with kinetochore) Sister chromatids
remain attached
Centrosome
(with centriole
Cleavage
pair)
furrow
Chiasmata Metaphase
Spindle
plate
Fragments
of nuclear
envelope
Homologous
chromosomes
© 2014 Pearson Education, Inc.
Homologous
chromosomes
separate
Microtubule
attached to
kinetochore
Figure 10.8b
MEIOSIS II: Separates sister chromatids
Prophase II
Metaphase II
Anaphase II
Telophase II and
Cytokinesis
Sister chromatids
separate
Haploid
daughter
cells forming
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 In synapsis, homologous chromosomes loosely pair
up, aligned gene by gene
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 In crossing over, nonsister chromatids exchange
DNA segments
 Crossing over produces recombinant
chromosomes, which combine DNA
from each parent
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 3 events unique to meiosis, all in meiosis l
 Synapsis and crossing over
 Homologous pairs at the metaphase plate:
 Separation of homologs
© 2014 Pearson Education, Inc.
Figure 10.9a
MITOSIS
MEIOSIS
Parent cell
Chiasma
MEIOSIS I
Prophase I
Prophase
Duplicated
chromosome
Metaphase
Anaphase
Telophase
2n
Daughter cells
of mitosis
© 2014 Pearson Education, Inc.
Chromosome
duplication
2n = 6
Chromosome
duplication
Individual
chromosomes
line up.
Pairs of
chromosomes
line up.
Sister chromatids
separate.
Homologs
separate.
2n
Sister
chromatids
separate.
Homologous
chromosome
pair
Metaphase I
Anaphase I
Telophase I
Daughter
cells of
meiosis I
MEIOSIS II
n
n
n
n
Daughter cells of meiosis II
Figure 10.9aa
MITOSIS
Prophase
Duplicated
chromosome
MEIOSIS
Parent cell
Chromosome
Chromosome
duplication 2n = 6 duplication
Individual
chromosomes
line up.
Metaphase
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Chiasma
Pairs of
chromosomes
line up.
MEIOSIS I
Prophase I
Homologous
chromosome
pair
Metaphase I
Figure 10.9ab
MEIOSIS
MITOSIS
Anaphase
Telophase
Sister chromatids
separate.
2n
Daughter cells
of mitosis
© 2014 Pearson Education, Inc.
2n
Anaphase I
Telophase I
Homologs
separate.
Sister
chromatids
separate.
Daughter
cells of
meiosis I
MEIOSIS II
n
n
n
n
Daughter cells of meiosis II
Figure 10.9b
SUMMARY
Property
Mitosis
Meiosis
DNA
replication
Occurs during interphase
before mitosis begins
Occurs during interphase before meiosis I
begins
Number of
divisions
One, including prophase,
prometaphase, metaphase,
anaphase, and telophase
Two, each including prophase, metaphase,
anaphase, and telophase
Synapsis of
homologous
chromosomes
Does not occur
Occurs during prophase I along with crossing
over between nonsister chromatids; resulting
chiasmata hold pairs together due to sister
chromatid cohesion
Number of
daughter cells
and genetic
composition
Two, each diploid (2n) and
genetically identical to the
parent cell
Four, each haploid (n), containing half as
many chromosomes as the parent cell;
genetically different from the parent cell and
from each other
Role in the
animal body
Enables multicellular adult to
arise from zygote; produces
cells for growth, repair, and,
in some species, asexual
reproduction
Produces gametes; reduces number of
chromosome sets by half and introduces
genetic variability among the gametes
© 2014 Pearson Education, Inc.
Concept 10.4: Genetic variation produced in
sexual life cycles contributes to evolution
 Mutations …the original source of genetic diversity
 Mutations create different alleles
 Reshuffling alleles produces genetic variation
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Origins of Genetic Variation Among Offspring
 meiotic mechanisms that contribute to genetic
variation

Independent assortment of chromosomes

Crossing over

Random fertilization
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Possible Chromosome Combinations
As a result of random alignment, the number of
possible combinations of chromosomes in a gamete
is:
2n
(and this is without crossing over)
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Possible Chromosome Combinations
2n for humans would be …
223 or…
8,388,608
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Figure 10.10-1
Possibility 2
Possibility 1
Two equally probable
arrangements of
chromosomes at
metaphase I
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Figure 10.10-2
Possibility 2
Possibility 1
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
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Figure 10.10-3
Possibility 2
Possibility 1
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Daughter
cells
Combination 1 Combination 2
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Combination 3 Combination 4
1
2
3
combinations possible
or
Possible
Chromosome
Combinations
or
or
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Fig. 10-7, p.161
Figure 10.11-1
Prophase I
of meiosis
Crossing
over
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Pair of
homologs
Nonsister chromatids
held together
during synapsis
Figure 10.11-2
Prophase I
of meiosis
Crossing
over
Pair of
homologs
Chiasma
Centromere
TEM
© 2014 Pearson Education, Inc.
Nonsister chromatids
held together
during synapsis
Synapsis and
crossing over
Figure 10.11-3
Prophase I
of meiosis
Crossing
over
Pair of
homologs
Chiasma
Nonsister chromatids
held together
during synapsis
Synapsis and
crossing over
Centromere
TEM
Anaphase I
© 2014 Pearson Education, Inc.
Breakdown of
proteins holding sister
chromatid arms together
Figure 10.11-4
Prophase I
of meiosis
Crossing
over
Pair of
homologs
Chiasma
Nonsister chromatids
held together
during synapsis
Synapsis and
crossing over
Centromere
TEM
Anaphase I
Anaphase II
© 2014 Pearson Education, Inc.
Breakdown of
proteins holding sister
chromatid arms together
Figure 10.11-5
Prophase I
of meiosis
Crossing
over
Pair of
homologs
Chiasma
Nonsister chromatids
held together
during synapsis
Synapsis and
crossing over
Centromere
TEM
Anaphase I
Breakdown of
proteins holding sister
chromatid arms together
Anaphase II
Daughter
cells
Recombinant chromosomes
© 2014 Pearson Education, Inc.
Random Fertilization
 Random fertilization adds to genetic variation
 fusion of 2 gametes (each with 8.4 million possible
combinations (from independent assortment))
produces zygote with 70 trillion diploid combinations
© 2014 Pearson Education, Inc.