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

2. Overview: Variations on a Theme
Living organisms are distinguished by their ability to reproduce their own kind
Heredity is the transmission of traits from one generation to the next
Variation is demonstrated by the differences in appearance that offspring show from parents and siblings
Genetics is the scientific study of heredity and variation
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3. Figure 10.1 What accounts for family resemblance?
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4. Concept 10.1: Offspring acquire genes from parents by inheriting chromosomes
In a literal sense, children do not inherit particular physical traits from their parents
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5. Inheritance of Genes
Genes are the units of heredity and are made up of segments of DNA
Genes are passed to the next generation via reproductive cells called gametes (sperm and eggs)
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6. Most DNA is packaged into chromosomes
For example, humans have 46 chromosomes in their somatic cells, the cells of the body except for gametes and their precursors
Each gene has a specific position, or locus, on a certain chromosome
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7. Comparison of Asexual and Sexual Reproduction
In asexual reproduction, a single individual passes genes to its offspring without the fusion of gametes
A clone is a group of genetically identical individuals from the same parent
In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents
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8. 0.5 mm Parent Bud (a) Hydra (b) Redwoods Figure 10.2
Figure 10.2 Asexual reproduction in two multicellular organisms
Bud
(a) Hydra
(b) Redwoods
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9. Concept 10.2: Fertilization and meiosis alternate in sexual life cycles
A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism
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10. Sets of Chromosomes in Human Cells
Human somatic cells have 23 pairs of chromosomes
A karyotype is an ordered display of the pairs of chromosomes from a cell
The two chromosomes in each pair are called homologous chromosomes, or homologs
Chromosomes in a homologous pair are the same length and shape and carry genes controlling the same inherited characters
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11. duplicated chromosomes
Figure 10.3
Technique
Results
Pair of homologous
duplicated chromosomes
Centromere
5 m
Sister
chromatids
Metaphase
chromosome
Figure 10.3 Research method: preparing a karyotype
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12. Figure
Technique
Figure Research method: preparing a karyotype (part 1: technique)
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13. duplicated chromosomes
Figure
Results
Pair of homologous
duplicated chromosomes
Centromere
5 m
Sister
chromatids
Figure Research method: preparing a karyotype (part 2: results)
Metaphase
chromosome
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14. Human females have a homologous pair of X chromosomes (XX)
The sex chromosomes, which determine the sex of the individual, are called X and Y
Human females have a homologous pair of X chromosomes (XX)
Human males have one X and one Y chromosome
The remaining 22 pairs of chromosomes are called autosomes
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15. A diploid cell (2n) has two sets of chromosomes
Each pair of homologous chromosomes includes one chromosome from each parent
The 46 chromosomes in a human somatic cell are two sets of 23: one from the mother and one from the father
A diploid cell (2n) has two sets of chromosomes
For humans, the diploid number is 46 (2n  46)
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16. Each replicated chromosome consists of two identical sister chromatids
In a cell in which DNA synthesis has occurred, each chromosome is replicated
Each replicated chromosome consists of two identical sister chromatids
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17. 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)
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18. For humans, the haploid number is 23 (n = 23)
A gamete (sperm or egg) contains a single set of chromosomes and is haploid (n)
For humans, the haploid number is 23 (n = 23)
Each set of 23 consists of 22 autosomes and a single sex chromosome
In an unfertilized egg (ovum), the sex chromosome is X
In a sperm cell, the sex chromosome may be either X or Y
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19. Behavior of Chromosome Sets in the Human Life Cycle
Fertilization is the union of gametes (the sperm and the egg)
The fertilized egg is called a zygote and has one set of chromosomes from each parent
The zygote produces somatic cells by mitosis and develops into an adult
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20. At sexual maturity, the ovaries and testes produce haploid gametes
Gametes are the only types of human cells produced by meiosis rather than mitosis
Meiosis results in one set of chromosomes in each gamete
Fertilization and meiosis alternate in sexual life cycles to maintain chromosome number
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21. MEIOSIS Key Haploid gametes (n = 23) Haploid (n) Egg (n) Diploid (2n)
Figure 10.5
Key
Haploid gametes (n = 23)
Haploid (n)
Egg (n)
Diploid (2n)
Sperm (n)
MEIOSIS
FERTILIZATION
Testis
Ovary
Figure 10.5 The human life cycle
Diploid
zygote
(2n = 46)
Mitosis and
development
Multicellular diploid
adults (2n = 46)
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22. The Variety of Sexual Life Cycles
The alternation of meiosis and fertilization is common to all organisms that reproduce sexually
The three main types of sexual life cycles differ in the timing of meiosis and fertilization
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23. Gametes are the only haploid cells in animals
They are produced by meiosis and undergo no further cell division before fertilization
Gametes fuse to form a diploid zygote that divides by mitosis to develop into a multicellular organism
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24. Haploid (n) Diploid (2n) Gametes n n n MEIOSIS FERTILIZATION Zygote 2n
Figure
Haploid (n)
Diploid (2n)
Gametes n n n
MEIOSIS
FERTILIZATION
Zygote
Figure Three types of sexual life cycles (part 1: animal) 2n 2n
Diploid
multicellular
organism
Mitosis
(a) Animals
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25. Plants and some algae exhibit an alternation of generations
This life cycle includes both a diploid and haploid multicellular stage
The diploid organism, called the sporophyte, makes haploid spores by meiosis
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26. A gametophyte makes haploid gametes by mitosis
Each spore grows by mitosis into a haploid organism called a gametophyte
A gametophyte makes haploid gametes by mitosis
Fertilization of gametes results in a diploid sporophyte
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27. (b) Plants and some algae
Figure
Haploid multi-
cellular organism
(gametophyte)
Haploid (n)
Diploid (2n)
Mitosis n
Mitosis n n n n
Spores
Gametes
MEIOSIS
FERTILIZATION
Figure Three types of sexual life cycles (part 2: plant) 2n 2n
Diploid
multicellular
organism
(sporophyte)
Zygote
Mitosis
(b) Plants and some algae
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28. The zygote produces haploid cells by meiosis
In most fungi and some protists, the only diploid stage is the single-celled zygote; there is no multicellular diploid stage
The zygote produces haploid cells by meiosis
Each haploid cell grows by mitosis into a haploid multicellular organism
The haploid adult produces gametes by mitosis
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29. Haploid unicellular or multicellular organism Haploid (n) Diploid (2n)
Figure
Haploid unicellular or
multicellular organism
Haploid (n)
Diploid (2n)
Mitosis n
Mitosis n n n
Gametes n
MEIOSIS
FERTILIZATION
Figure Three types of sexual life cycles (part 3: fungi) 2n
Zygote
(c) Most fungi and some protists
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30. However, only diploid cells can undergo meiosis
Depending on the type of life cycle, either haploid or diploid cells can divide by mitosis
However, only diploid cells can undergo meiosis
In all three life cycles, the halving and doubling of chromosomes contribute to genetic variation in offspring
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31. Concept 10.3: Meiosis reduces the number of chromosome sets from diploid to haploid
Like mitosis, meiosis is preceded by the duplication of chromosomes
Meiosis takes place in two sets of cell divisions, called meiosis I and meiosis II
The two cell divisions result in four daughter cells, rather than the two daughter cells in mitosis
Each daughter cell has only half as many chromosomes as the parent cell
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32. The Stages of Meiosis
For a single pair of homologous chromosomes in a diploid cell, both members of the pair are duplicated
The resulting sister chromatids are closely associated all along their lengths
Homologs may have different versions of genes, each called an allele
Homologs are not associated in any obvious way except during meiosis
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33. duplicated chromosomes Meiosis II
Figure 10.7
Interphase
Pair of homologous
chromosomes in
diploid parent cell
Pair of duplicated
homologous
chromosomes
Chromosomes
duplicate
Sister
chromatids
Diploid cell with
duplicated
chromosomes
Meiosis I
Homologous
chromosomes
separate
Figure 10.7 Overview of meiosis: how meiosis reduces chromosome number
Haploid cells with
duplicated chromosomes
Meiosis II
Sister chromatids
separate
Haploid cells with unduplicated chromosomes
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34. Interphase Pair of homologous chromosomes in diploid parent cell
Figure
Interphase
Pair of homologous
chromosomes in
diploid parent cell
Pair of duplicated
homologous
chromosomes
Chromosomes
duplicate
Figure Overview of meiosis: how meiosis reduces chromosome number (part 1: interphase)
Sister
chromatids
Diploid cell with
duplicated
chromosomes
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35. duplicated chromosomes Meiosis II
Figure
Meiosis I
Homologous
chromosomes
separate
Haploid cells with
duplicated chromosomes
Meiosis II
Sister chromatids
separate
Figure Overview of meiosis: how meiosis reduces chromosome number (part 2: meiosis I and II)
Haploid cells with unduplicated chromosomes
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36. Meiosis halves the total number of chromosomes very specifically
It reduces the number of sets from two to one, with each daughter cell receiving one set of chromosomes
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37. Four new haploid cells are produced as a result
In the first meiotic division, homologous pairs of chromosomes pair and separate
In the second meiotic division, sister chromatids of each chromosome separate
Four new haploid cells are produced as a result
NOTE – this is not part of the text, but rather a quick summary of what is in Figure 10.8.
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38. Separates homologous chromosomes Separates sister chromatids
Figure 10.8
MEIOSIS I:
MEIOSIS II:
Separates homologous chromosomes
Separates sister chromatids
Telophase I
and Cytokinesis
Telophase II
and Cytokinesis
Prophase I
Metaphase I
Anaphase I
Prophase II
Metaphase II
Anaphase II
Figure 10.8 Exploring meiosis in an animal cell
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39. MEIOSIS I: Separates homologous chromosomes
Figure
MEIOSIS I: Separates homologous chromosomes
Telophase I
and Cytokinesis
Prophase I
Metaphase I
Anaphase I
Sister chromatids
remain attached
Centrosome
(with centriole pair)
Kinetochore
(at centromere)
Sister
chromatids
Chiasmata
Spindle
microtubules
Kinetochore
microtubules
Metaphase
plate
Figure Exploring meiosis in an animal cell (part 1: meiosis I)
Cleavage
furrow
Fragments
of nuclear
envelope
Homologous
chromosomes
separate
Pair of
homologous
chromosomes
Centromere
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40. Separates homologous chromosomes
Figure a
MEIOSIS I:
Separates homologous chromosomes
Prophase I
Metaphase I
Centrosome
(with centriole pair)
Kinetochore
(at centromere)
Sister
chromatids
Chiasmata
Kinetochore
microtubules
Spindle
microtubules
Metaphase
plate
Figure a Exploring meiosis in an animal cell (part 1a: prophase I and metaphase I)
Fragments
of nuclear
envelope
Pair of
homologous
chromosomes
Centromere
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41. Separates homologous chromosomes
Figure b
MEIOSIS I:
Separates homologous chromosomes
Telophase I
and Cytokinesis
Anaphase I
Sister chromatids
remain attached
Figure b Exploring meiosis in an animal cell (part 1b: anaphase I, telophase I and cytokinesis)
Cleavage
furrow
Homologous
chromosomes
separate
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42. MEIOSIS II: Separates sister chromatids
Figure
MEIOSIS II: Separates sister chromatids
Telophase II
and Cytokinesis
Prophase II
Metaphase II
Anaphase II
Sister chromatids
separate
Figure Exploring meiosis in an animal cell (part 2: meiosis II)
Haploid daughter
cells forming
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43. Chromosomes condense progressively throughout prophase I
Homologous chromosomes pair up, aligned gene by gene
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44. In crossing over, nonsister chromatids exchange DNA segments
Each homologous pair has one or more X-shaped regions called chiasmata
Chiasmata exist at points where crossing over has occurred.
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45. Metaphase I
In metaphase I, homologous pairs line up at the metaphase plate, with one chromosome facing each pole
Microtubules from one pole are attached to the kinetochore of one chromosome of each tetrad
Microtubules from the other pole are attached to the kinetochore of the other chromosome
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46. In anaphase I, pairs of homologous chromosomes separate
One chromosome moves toward each pole, guided by the spindle apparatus
Sister chromatids remain attached at the centromere and move as one unit toward the pole
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47. Telophase I and Cytokinesis
In the beginning of telophase I, each half of the cell has a haploid set of chromosomes
Each chromosome still consists of two sister chromatids
Cytokinesis usually occurs simultaneously, forming two haploid daughter cells
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48. In animal cells, a cleavage furrow forms; in plant cells, a cell plate forms
No chromosome duplication occurs between the end of meiosis I and the beginning of meiosis II because the chromosomes are already replicated
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49. Division in meiosis II also occurs in four phases
Prophase II
Metaphase II
Anaphase II
Telophase II and cytokinesis
Meiosis II is very similar to mitosis
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50. In prophase II, a spindle apparatus forms
In late prophase II, chromosomes (each still composed of two chromatids) move toward the metaphase plate
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51. The sister chromatids are arranged at the metaphase plate
Metaphase II
The sister chromatids are arranged at the metaphase plate
Because of crossing over in meiosis I, the two sister chromatids of each chromosome are no longer genetically identical
The kinetochores of sister chromatids attach to microtubules extending from opposite poles
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52. In anaphase II, the sister chromatids separate
The sister chromatids of each chromosome now move as two newly individual chromosomes toward opposite poles
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53. Telophase II and Cytokinesis
Nuclei form, and the chromosomes begin decondensing
At the end of meiosis, there are four daughter cells, each with a haploid set of unduplicated chromosomes
Each daughter cell is genetically distinct from the others and from the parent cell
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54. Crossing Over and Synapsis During Prophase I
During prophase I, two members of a homologous pair associate along their length, allele by allele
A zipper-like structure called the synaptonemal complex forms during this attachment (synapsis)
DNA molecules of the maternal and paternal chromatid are broken at matching points
The DNA breaks are closed so that a paternal chromatid is joined to a piece of maternal chromatid, and vice versa
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55. DNA breaks Centromere DNA breaks Paternal sister chromatids Cohesins
Figure 10.9
Pair of homologous
chromosomes:
DNA
breaks
Centromere
DNA
breaks
Paternal
sister
chromatids
Cohesins
Maternal
sister
chromatids
Synaptonemal
complex forming
Synaptonemal
complex
Crossover
Crossover
Figure 10.9 Crossing over and synapsis in prophase I (part 1: cohesins and the synaptonemal complex)
Chiasmata
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56. DNA Centromere DNA breaks breaks Paternal sister Cohesins chromatids
Figure
Pair of homologous
chromosomes:
DNA
breaks
Centromere
DNA
breaks
Paternal
sister
chromatids
Cohesins
Maternal
sister
chromatids
Synaptonemal
complex forming
Figure Crossing over and synapsis in prophase I (part 2: synapsis and chiasmata)
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57. Synaptonemal complex Crossover Crossover Chiasmata Figure 10.9-2
Figure Crossing over and synapsis in prophase I
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58. A Comparison of Mitosis and Meiosis
Mitosis conserves the number of chromosome sets, producing cells that are genetically identical to the parent cell
Meiosis reduces the number of chromosome sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell
Meiosis includes two divisions after replication, each with specific stages
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59. Three events are unique to meiosis, and all three occur in meiosis l
Synapsis and crossing over in prophase I: Homologous chromosomes physically connect and exchange genetic information
Alignment of homologous pairs at the metaphase plate: Homologous pairs of chromosomes are positioned there in metaphase I
Separation of homologs during anaphase I
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60. Sister chromatids stay together due to sister chromatid cohesion
In mitosis, cohesins are cleaved at the end of metaphase
In meiosis, cohesins are cleaved along the chromosome arms in anaphase I (separation of homologs) and at the centromeres in anaphase II (separation of sister chromatids)
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61. Figure 10.10 A comparison of mitosis and meiosis SUMMARY
Parent cell
Chiasma
MEIOSIS I
Prophase
Prophase I
Pair of duplicated
homologs
Chromosome
duplication
Chromosome
duplication
Duplicated
chromosome
2n = 6
Individual
chromosomes
line up.
Pairs of
chromosomes
line up.
Metaphase
Metaphase I
Anaphase
Anaphase I
Sister chromatids
separate.
Homologs
separate.
Telophase
Telophase I
Haploid
n = 3
Daughter
cells of
meiosis I
Sister
chromatids
separate.
MEIOSIS II 2n 2n
Daughter cells
of mitosis n n n n
Daughter cells of meiosis II
Figure A comparison of mitosis and meiosis
SUMMARY
Property
Mitosis (diploid and haploid)
Meiosis (diploid only)
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
Does not occur
Two, each including prophase, metaphase, anaphase, and telophase
Synapsis of homologous
chromosomes
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 genetically identical to the parent
cell, with the same number of chromosomes
Four, each haploid (n); genetically different from the parent
cell and from each other
Role in the animal or
plant body
Enables multicellular animal or plant
(gametophyte or sporophyte) to arise from a
single cell; produces cells for growth, repair,
and, in some species, asexual reproduction;
produces gametes in the gametophyte plant
Produces gametes (in animals) or spores (in the sporophyte plant);
reduces number of chromosome sets by half and introduces
genetic variability among the gametes or spores
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62. Daughter cells of meiosis II
Figure
MITOSIS
MEIOSIS
Parent cell
Chiasma
MEIOSIS I
Prophase
Prophase I
Chromosome
duplication
Chromosome
duplication
Pair of duplicated
homologs
Duplicated
chromosome
2n = 6
Pairs of
chromosomes
line up.
Individual
chromosomes
line up.
Metaphase
Metaphase I
Anaphase
Anaphase I
Sister chromatids
separate.
Homologs
separate.
Telophase
Telophase I
Haploid
Figure A comparison of mitosis and meiosis (part 1: mitosis vs. meiosis art)
n = 3
Daughter
cells of
meiosis I
Sister
chromatids
separate.
MEIOSIS II 2n 2n
Daughter cells
of mitosis n n n n
Daughter cells of meiosis II
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63. Chromosome duplication Chromosome duplication
Figure a
MITOSIS
MEIOSIS
Parent cell
Chiasma
MEIOSIS I
Prophase
Prophase I
Pair of
duplicated
homologs
Chromosome
duplication
Chromosome
duplication
Duplicated
chromosome
2n = 6
Pairs of
chromosomes
line up.
Individual
chromosomes
line up.
Metaphase
Metaphase I
Figure a A comparison of mitosis and meiosis (part 1a: prophase and metaphase art)
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64. Daughter cells of mitosis
Figure b
MITOSIS
MEIOSIS
Anaphase
Anaphase I
Telophase
Telophase I
Sister chromatids
separate.
Homologs
separate.
Haploid
n = 3
Sister
chromatids
separate.
Daughter
cells of
meiosis I
MEIOSIS II 2n 2n n n n n
Figure b A comparison of mitosis and meiosis (part 1b: anaphase, telophase and meiosis II art)
Daughter cells
of mitosis
Daughter cells of meiosis II
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65. Figure
Figure A comparison of mitosis and meiosis (part 2: mitosis vs. meiosis table)
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66. Figure a
Figure a A comparison of mitosis and meiosis (part 2a: mitosis table)
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67. Figure b
Figure b A comparison of mitosis and meiosis (part 2b: meiosis table)
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68. Concept 10.4: Genetic variation produced in sexual life cycles contributes to evolution
Mutations (changes in an organism’s DNA) are the original source of genetic diversity
Mutations create different versions of genes called alleles
Reshuffling of alleles during sexual reproduction produces genetic variation
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69. Origins of Genetic Variation Among Offspring
The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises in each generation
Three mechanisms contribute to genetic variation
Independent assortment of chromosomes
Crossing over
Random fertilization
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70. Independent Assortment of Chromosomes
Homologous pairs of chromosomes orient randomly at metaphase I of meiosis
In independent assortment, each pair of chromosomes sorts maternal and paternal homologs into daughter cells independently of the other pairs
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71. The number of combinations possible when chromosomes assort independently into gametes is 2n, where n is the haploid number
For humans (n = 23), there are more than 8 million (223) possible combinations of chromosomes
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72. Possibility 1 Possibility 2 Two equally probable arrangements of
Figure s1
Possibility 1
Possibility 2
Two equally probable
arrangements of
chromosomes at
metaphase I
Figure s1 The independent assortment of homologous chromosomes in meiosis (step 1)
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73. Possibility 1 Possibility 2 Two equally probable arrangements of
Figure s2
Possibility 1
Possibility 2
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Figure s2 The independent assortment of homologous chromosomes in meiosis (step 2)
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74. Possibility 1 Possibility 2 Two equally probable arrangements of
Figure s3
Possibility 1
Possibility 2
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Figure s3 The independent assortment of homologous chromosomes in meiosis (step 3)
Daughter
cells
Combination 2
Combination 1
Combination 3
Combination 4
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75. Crossing Over
Crossing over produces recombinant chromosomes, which combine DNA inherited from each parent
In meiosis in humans, on average, one to three crossover events occur per chromosome pair
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76. Crossing over contributes to genetic variation by combining DNA, producing chromosomes with new combinations of maternal and paternal alleles
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77. Nonsister chromatids held together Prophase I during synapsis
Figure s1
Nonsister chromatids
held together
during synapsis
Prophase I
of meiosis
Pair of
homologs
Figure s1 The results of crossing over during meiosis (step 1)
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78. Nonsister chromatids held together Prophase I during synapsis
Figure s2
Nonsister chromatids
held together
during synapsis
Prophase I
of meiosis
Pair of
homologs
Synapsis and
crossing over
Chiasma
site
Centromere
TEM
Figure s2 The results of crossing over during meiosis (step 2)
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79. proteins holding sister chromatid arms together. Centromere
Figure s3
Nonsister chromatids
held together
during synapsis
Prophase I
of meiosis
Pair of
homologs
Synapsis and
crossing over
Chiasma
site
Breakdown of
proteins holding sister
chromatid arms together.
Centromere
TEM
Anaphase I
Figure s3 The results of crossing over during meiosis (step 3)
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80. proteins holding sister chromatid arms together. Centromere
Figure s4
Nonsister chromatids
held together
during synapsis
Prophase I
of meiosis
Pair of
homologs
Synapsis and
crossing over
Chiasma
site
Breakdown of
proteins holding sister
chromatid arms together.
Centromere
TEM
Anaphase I
Figure s4 The results of crossing over during meiosis (step 4)
Anaphase II
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81. proteins holding sister chromatid arms together. Centromere
Figure s5
Nonsister chromatids
held together
during synapsis
Prophase I
of meiosis
Pair of
homologs
Synapsis and
crossing over
Chiasma
site
Breakdown of
proteins holding sister
chromatid arms together.
Centromere
TEM
Anaphase I
Figure s5 The results of crossing over during meiosis (step 5)
Anaphase II
Daughter
cells
Recombinant chromosomes
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82. Chiasma site Centromere TEM Figure 10.12-1
Figure The results of crossing over during meiosis (part 1: TEM)
TEM
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83. Random Fertilization
Random fertilization adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg)
The fusion of two gametes (each with 8.4 million possible chromosome combinations from independent assortment) produces a zygote with any of about 70 trillion diploid combinations
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84. Crossing over adds even more variation
Each zygote has a unique genetic identity
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85. The Evolutionary Significance of Genetic Variation Within Populations
Natural selection results in the accumulation of genetic variations favored by the environment
Sexual reproduction contributes to the genetic variation in a population, which originates from mutations
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86. Asexual reproduction is less expensive than sexual reproduction
Nonetheless, sexual reproduction is nearly universal among animals
Overall, genetic variation is evolutionarily advantageous
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87. Figure 10.UN01-1
Figure 10.UN01-1 Skills exercise: making a line graph and converting between units of data (part 1)
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88. Prophase I: Each pair of homologous chromosomes
Figure 10.UN02
Prophase I: Each pair of homologous chromosomes
undergoes synapsis and crossing over between
nonsister chromatids with the subsequent appearance
of chiasmata.
Metaphase I: Chromosomes line up as homologous
pairs on the metaphase plate.
Figure 10.UN02 Summary of key concepts: three events of meiosis I unique to meiosis
Anaphase I: Homologs separate from each other;
sister chromatids remain joined at the centromere.
© 2016 Pearson Education, Inc.

89. Figure 10.UN03 F H
Figure 10.UN03 Test your understanding, question 6 (cell in meiosis)
© 2016 Pearson Education, Inc.