1. Meiosis and Sexual Life Cycles10
Meiosis and Sexual Life Cycles

2. Inheritance of Genes
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3. Sets of Chromosomes in Human Cells
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4. duplicated chromosomes
Figure 10.3
Application
Technique
Pair of homologous
duplicated chromosomes
5 m
Centromere
Sister
chromatids
Figure 10.3 Research method: preparing a karyotype
Metaphase
chromosome 4

5. _________________________________________5

6. Key Maternal set of chromosomes (n  3) 2n  6 Paternal set of
Figure 10.4
Key
Maternal set of
chromosomes (n  3)
2n  6
Paternal set of
chromosomes (n  3)
Sister chromatids
of one duplicated
chromosome
Centromere
Figure 10.4 Describing chromosomes
Two nonsister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set) 6

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

8. Key Haploid (n) n Gametes n Diploid (2n) n MEIOSIS FERTILIZATION
Figure 10.6a
Key
Haploid (n) n
Gametes n
Diploid (2n) n
MEIOSIS
FERTILIZATION
Zygote 2n 2n
Figure 10.6a Three types of sexual life cycles (part 1: animal)
Mitosis
Diploid
multicellular
organism
(a) Animals 8

9. (b) Plants and some algae
Figure 10.6b
Haploid multi-
cellular organism
(gametophyte)
Key
Haploid (n)
Diploid (2n)
Mitosis n
Mitosis n n n n
Spores
Gametes
MEIOSIS
FERTILIZATION 2n
Figure 10.6b Three types of sexual life cycles (part 2: plant) 2n
Zygote
Diploid
multicellular
organism
(sporophyte)
Mitosis
(b) Plants and some algae 9

10. Haploid unicellular or multicellular organism Key
Figure 10.6c
Haploid unicellular or
multicellular organism
Key
Haploid (n)
Diploid (2n)
Mitosis n
Mitosis n n n
Gametes n
MEIOSIS
FERTILIZATION
Figure 10.6c Three types of sexual life cycles (part 3: fungi) 2n
Zygote
(c) Most fungi and some protists 10

11. Concept 10.3: Meiosis reduces the number of chromosome sets from diploid to haploid
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(that become gametes) 11

12. duplicated chromosomes Meiosis II
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
Figure 10.7 Overview of meiosis: how meiosis reduces chromosome number
Haploid cells with
duplicated chromosomes
Meiosis II 2
Sister chromatids
separate
Haploid cells with unduplicated chromosomes 12

13. Interphase Pair of homologous chromosomes in diploid parent cell
Figure 10.7a
Interphase
Pair of homologous
chromosomes in
diploid parent cell
Chromosomes
duplicate
Duplicated pair
of homologous
chromosomes
Figure 10.7a Overview of meiosis: how meiosis reduces chromosome number (part 1: interphase)
Sister
chromatids
Diploid cell with
duplicated
chromosomes 13

14. duplicated chromosomes Meiosis II 2 Sister chromatids separate
Figure 10.7b
Meiosis I 1
Homologous
chromosomes
separate
Haploid cells with
duplicated chromosomes
Meiosis II 2
Sister chromatids
separate
Figure 10.7b Overview of meiosis: how meiosis reduces chromosome number (part 2: meiosis I and II)
Haploid cells with unduplicated chromosomes 14

15. __________________________________________
NOTE – this is not part of the text, but rather a quick summary of what is in Figure 10.8.
Animation: Meiosis
Video: Meiosis I in Sperm Formation 15

16. MEIOSIS I: Separates homologous chromosomes
Figure 10.8a
MEIOSIS I: Separates homologous chromosomes
Telophase I and
Cytokinesis
Prophase I
Metaphase I
Anaphase I
Sister
chromatids
Centromere
(with kinetochore)
Sister chromatids
remain attached
Centrosome
(with centriole
pair)
Cleavage
furrow
Chiasmata
Metaphase
plate
Spindle
Figure 10.8a Exploring meiosis in an animal cell (part 1: meiosis I)
Homologous
chromosomes
separate
Fragments
of nuclear
envelope
Microtubule
attached to
kinetochore
Homologous
chromosomes 16

17. MEIOSIS II: Separates sister chromatids
Figure 10.8b
MEIOSIS II: Separates sister chromatids
Telophase II and
Cytokinesis
Prophase II
Metaphase II
Anaphase II
Sister chromatids
separate
Figure 10.8b Exploring meiosis in an animal cell (part 2: meiosis II)
Haploid
daughter
cells forming 17

18. __________________________________________ __________________________________________18

19. _________________________________________
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20. __________________________________________
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21. Daughter cells of meiosis II
Figure 10.9a
MITOSIS
MEIOSIS
Parent cell
Chiasma
MEIOSIS I
Prophase
Prophase I
Chromosome
duplication
Chromosome
duplication
Homologous
chromosome
pair
Duplicated
chromosome
2n = 6
Individual
chromosomes
line up.
Pairs of
chromosomes
line up.
Metaphase
Metaphase I
Anaphase
Sister chromatids
separate.
Homologs
separate.
Anaphase I
Telophase
Telophase I
Figure 10.9a A comparison of mitosis and meiosis in diploid cells (part 1: mitosis vs. meiosis art)
Sister
chromatids
separate.
Daughter
cells of
meiosis I 2n 2n
MEIOSIS II
Daughter cells
of mitosis n n n n
Daughter cells of meiosis II 21

22. Chromosome duplication Chromosome duplication
Figure 10.9aa
MITOSIS
MEIOSIS
MEIOSIS I
Parent cell
Prophase
Chiasma
Prophase I
Homologous
chromosome
pair
Duplicated
chromosome
Chromosome
duplication
Chromosome
duplication
2n = 6
Individual
chromosomes
line up.
Pairs of
chromosomes
line up.
Figure 10.9aa A comparison of mitosis and meiosis in diploid cells (part 1a: prophase and metaphase art)
Metaphase I
Metaphase 22

23. Daughter cells of mitosis
Figure 10.9ab
MITOSIS
MEIOSIS
Anaphase
Anaphase I
Telophase
Telophase I
Sister chromatids
separate.
Homologs
separate.
Sister
chromatids
separate.
Daughter
cells of
meiosis I
MEIOSIS II 2n 2n n n
Figure 10.9ab A comparison of mitosis and meiosis in diploid cells (part 1b: anaphase, telophase and meiosis II art)
Daughter cells
of mitosis n n
Daughter cells of meiosis II 23

24. SUMMARY Property Mitosis Meiosis DNA replication
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
Figure 10.9b A comparison of mitosis and meiosis in diploid cells (part 2: mitosis vs. meiosis table)
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 24

25. Concept 10.4: Genetic variation produced in sexual life cycles contributes to evolution
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26. Origins of Genetic Variation Among Offspring
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27. Possible Chromosome Combinations
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28. Possible Chromosome Combinations
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29. Possibility 2 Possibility 1 Two equally probable arrangements of
Figure
Possibility 1
Possibility 2
Two equally probable
arrangements of
chromosomes at
metaphase I
Figure The independent assortment of homologous chromosomes in meiosis (step 1) 29

30. Possibility 2 Possibility 1 Two equally probable arrangements of
Figure
Possibility 1
Possibility 2
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Figure The independent assortment of homologous chromosomes in meiosis (step 2) 30

31. Possibility 1 Possibility 2 Two equally probable arrangements of
Figure
Possibility 1
Possibility 2
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Figure The independent assortment of homologous chromosomes in meiosis (step 3)
Daughter
cells
Combination 1
Combination 2
Combination 3
Combination 4 31

32. combinations possible
Possible Chromosome Combinations 1 2 3
combinations possible or or or
Fig. 10-7, p.161

33. Crossing over Prophase I of meiosis Nonsister chromatids held together
Figure
Prophase I
of meiosis
Nonsister chromatids
held together
during synapsis
Pair of
homologs
Crossing
over
Figure The results of crossing over during meiosis (step 1) 33

34. Crossing over Prophase I of meiosis Nonsister chromatids held together
Figure
Prophase I
of meiosis
Nonsister chromatids
held together
during synapsis
Crossing
over
Pair of
homologs
Synapsis and
crossing over
Chiasma
Centromere
TEM
Figure The results of crossing over during meiosis (step 2) 34

35. Crossing over Prophase I of meiosis Nonsister chromatids held together
Figure
Prophase I
of meiosis
Nonsister chromatids
held together
during synapsis
Crossing
over
Pair of
homologs
Synapsis and
crossing over
Chiasma
Centromere
TEM
Breakdown of
proteins holding sister
chromatid arms together
Anaphase I
Figure The results of crossing over during meiosis (step 3) 35

36. Crossing over Prophase I of meiosis Nonsister chromatids held together
Figure
Prophase I
of meiosis
Nonsister chromatids
held together
during synapsis
Crossing
over
Pair of
homologs
Synapsis and
crossing over
Chiasma
Centromere
TEM
Breakdown of
proteins holding sister
chromatid arms together
Anaphase I
Figure The results of crossing over during meiosis (step 4)
Anaphase II 36

37. Crossing over Prophase I of meiosis Nonsister chromatids held together
Figure
Prophase I
of meiosis
Nonsister chromatids
held together
during synapsis
Crossing
over
Pair of
homologs
Synapsis and
crossing over
Chiasma
Centromere
TEM
Breakdown of
proteins holding sister
chromatid arms together
Anaphase I
Figure The results of crossing over during meiosis (step 5)
Anaphase II
Daughter
cells
Recombinant chromosomes 37

38. Random Fertilization ___________________________________
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(from independent assortment) ___________________________________ ___________________________________ 38