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Meiosis and Sexual Life Cycles презентация
Содержание
- 1. Meiosis and Sexual Life Cycles
- 2. Overview: Variations on a Theme Living organisms
- 3. Fig. 13-1
- 4. Concept 13.1: Offspring acquire genes from parents
- 5. Inheritance of Genes Genes are the units
- 6. Comparison of Asexual and Sexual Reproduction
- 7. Fig. 13-2 (a) Hydra (b) Redwoods Parent Bud 0.5 mm
- 8. Fig. 13-2a (a) Hydra 0.5 mm Bud Parent
- 9. Fig. 13-2b (b) Redwoods
- 10. Concept 13.2: Fertilization and meiosis alternate in
- 11. Sets of Chromosomes in Human Cells Human
- 12. Fig. 13-3 APPLICATION TECHNIQUE Pair
- 13. Fig. 13-3a APPLICATION
- 14. Fig. 13-3b TECHNIQUE Pair of homologous
- 15. The sex chromosomes are called X and
- 16. Each pair of homologous chromosomes includes one
- 17. In a cell in which DNA synthesis
- 18. Fig. 13-4 Key Maternal set of chromosomes
- 19. A gamete (sperm or egg) contains a
- 20. Fertilization is the union of gametes (the
- 21. At sexual maturity, the ovaries and testes
- 22. Fig. 13-5 Key Haploid (n) Diploid (2n)
- 23. The Variety of Sexual Life Cycles The
- 24. In animals, meiosis produces gametes, which undergo
- 25. Fig. 13-6 Key Haploid (n) Diploid (2n)
- 26. Fig. 13-6a Key Haploid (n) Diploid (2n)
- 27. Plants and some algae exhibit an alternation
- 28. Each spore grows by mitosis into a
- 29. Fig. 13-6b Key Haploid (n) Diploid (2n)
- 30. In most fungi and some protists, the
- 31. Fig. 13-6c Key Haploid (n) Diploid (2n)
- 32. Depending on the type of life cycle,
- 33. Concept 13.3: Meiosis reduces the number of
- 34. The Stages of Meiosis In the first
- 35. Fig. 13-7-1 Interphase Homologous pair of chromosomes
- 36. Fig. 13-7-2 Interphase Homologous pair of
- 37. Fig. 13-7-3 Interphase Homologous pair
- 38. Meiosis I is preceded by interphase, in
- 40. Division in meiosis I occurs in four
- 41. Metaphase I Fig.
- 42. Prophase I Prophase I typically occupies more
- 43. In crossing over, nonsister chromatids exchange DNA
- 44. Metaphase I In metaphase I, tetrads line
- 45. Fig. 13-8b Prophase I Metaphase
- 46. Anaphase I In anaphase I, pairs of
- 47. Telophase I and Cytokinesis In the beginning
- 48. In animal cells, a cleavage furrow forms;
- 49. Fig. 13-8c Anaphase I Telophase
- 50. Division in meiosis II also occurs in
- 51. Fig. 13-8d Prophase
- 52. Prophase II In prophase II, a spindle
- 53. Metaphase II In metaphase II, the sister
- 54. Fig. 13-8e Prophase II Metaphase II
- 55. Anaphase II In anaphase II, the sister
- 56. Telophase II and Cytokinesis In telophase II,
- 57. Cytokinesis separates the cytoplasm At the end
- 58. Fig. 13-8f Anaphase II Telephase
- 59. A Comparison of Mitosis and Meiosis Mitosis
- 60. Fig. 13-9 MITOSIS MEIOSIS MEIOSIS I Prophase
- 61. Fig. 13-9a MITOSIS MEIOSIS MEIOSIS I Prophase
- 62. Fig. 13-9b SUMMARY Meiosis Mitosis Property DNA
- 63. Three events are unique to meiosis, and
- 64. Sister chromatid cohesion allows sister chromatids of
- 65. Fig. 13-10 EXPERIMENT RESULTS Shugoshin+
- 66. Fig. 13-10a EXPERIMENT Shugoshin+ (normal) Spore
- 67. Fig. 13-10b RESULTS Shugoshin+ Shugoshin– Spore cases (%) 100 80 60 40 20 0
- 68. Concept 13.4: Genetic variation produced in sexual
- 69. Origins of Genetic Variation Among Offspring The
- 70. Independent Assortment of Chromosomes Homologous pairs of
- 71. The number of combinations possible when chromosomes
- 72. Fig. 13-11-1 Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I
- 73. Fig. 13-11-2 Possibility 1 Possibility 2 Two
- 74. Fig. 13-11-3 Possibility 1 Possibility 2 Two
- 75. Crossing Over Crossing over produces recombinant chromosomes,
- 76. In crossing over, homologous portions of two
- 77. Fig. 13-12-1 Prophase I of meiosis Pair
- 78. Fig. 13-12-2 Prophase I of meiosis Pair
- 79. Fig. 13-12-3 Prophase I of meiosis Pair
- 80. Fig. 13-12-4 Prophase I of meiosis Pair
- 81. Fig. 13-12-5 Prophase I of meiosis Pair
- 82. Random Fertilization Random fertilization adds to genetic
- 83. Crossing over adds even more variation Each
- 84. The Evolutionary Significance of Genetic Variation Within
- 85. Fig. 13-UN1 Prophase I: Each homologous pair
- 86. Fig. 13-UN2 F H
- 87. Fig. 13-UN3
- 88. Fig. 13-UN4
- 89. You should now be able to: Distinguish
Слайд 2Overview: Variations on a Theme
Living organisms are distinguished by their ability
Genetics is the scientific study of heredity and variation
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 4Concept 13.1: Offspring acquire genes from parents by inheriting chromosomes
In a
It is genes that are actually inherited
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 5Inheritance of Genes
Genes are the units of heredity, and are made
Genes are passed to the next generation through reproductive cells called gametes (sperm and eggs)
Each gene has a specific location called a locus on a certain chromosome
Most DNA is packaged into chromosomes
One set of chromosomes is inherited from each parent
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 6Comparison of Asexual and Sexual Reproduction
In asexual reproduction, one parent
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
Video: Hydra Budding
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 10Concept 13.2: Fertilization and meiosis alternate in sexual life cycles
A life
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 11Sets of Chromosomes in Human Cells
Human somatic cells (any cell other
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 carry genes controlling the same inherited characters
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 12
Fig. 13-3
APPLICATION
TECHNIQUE
Pair of homologous
replicated chromosomes
5 µm
Centromere
Sister
chromatids
Metaphase
chromosome
Слайд 14
Fig. 13-3b
TECHNIQUE
Pair of homologous
replicated chromosomes
Centromere
Sister
chromatids
Metaphase
chromosome
5 µm
Слайд 15The sex chromosomes are called X and Y
Human females have a
Human males have one X and one Y chromosome
The 22 pairs of chromosomes that do not determine sex are called autosomes
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 16Each pair of homologous chromosomes includes one chromosome from each parent
The
A diploid cell (2n) has two sets of chromosomes
For humans, the diploid number is 46 (2n = 46)
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 17In a cell in which DNA synthesis has occurred, each chromosome
Each replicated chromosome consists of two identical sister chromatids
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 18Fig. 13-4
Key
Maternal set of
chromosomes (n = 3)
Paternal set of
chromosomes (n =
2n = 6
Centromere
Two sister chromatids
of one replicated
chromosome
Two nonsister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set)
Слайд 19A gamete (sperm or egg) contains a single set of chromosomes,
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 20Fertilization is the union of gametes (the sperm and the egg)
The
The zygote produces somatic cells by mitosis and develops into an adult
Behavior of Chromosome Sets in the Human Life Cycle
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 21At sexual maturity, the ovaries and testes produce haploid gametes
Gametes are
Meiosis results in one set of chromosomes in each gamete
Fertilization and meiosis alternate in sexual life cycles to maintain chromosome number
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 22Fig. 13-5
Key
Haploid (n)
Diploid (2n)
Haploid gametes (n = 23)
Egg (n)
Sperm (n)
MEIOSIS
FERTILIZATION
Ovary
Testis
Diploid
zygote
(2n =
Mitosis and
development
Multicellular diploid
adults (2n = 46)
Слайд 23The Variety of Sexual Life Cycles
The alternation of meiosis and fertilization
The three main types of sexual life cycles differ in the timing of meiosis and fertilization
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 24In animals, meiosis produces gametes, which undergo no further cell division
Gametes are the only haploid cells in animals
Gametes fuse to form a diploid zygote that divides by mitosis to develop into a multicellular organism
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 25Fig. 13-6
Key
Haploid (n)
Diploid (2n)
n
n
Gametes
n
n
n
Mitosis
MEIOSIS
FERTILIZATION
MEIOSIS
2n
2n
Zygote
2n
Mitosis
Diploid
multicellular
organism
(a) Animals
Spores
Diploid
multicellular
organism
(sporophyte)
(b) Plants and some algae
2n
Mitosis
Gametes
Mitosis
n
n
n
Zygote
FERTILIZATION
n
n
n
Mitosis
Zygote
(c) Most fungi
MEIOSIS
FERTILIZATION
2n
Gametes
n
n
Mitosis
Haploid multi-
cellular organism
(gametophyte)
Haploid unicellular or
multicellular organism
Слайд 26Fig. 13-6a
Key
Haploid (n)
Diploid (2n)
Gametes
n
n
n
2n
2n
Zygote
MEIOSIS
FERTILIZATION
Mitosis
Diploid
multicellular
organism
(a) Animals
Слайд 27Plants and some algae exhibit an alternation of generations
This life cycle
The diploid organism, called the sporophyte, makes haploid spores by meiosis
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 28Each spore grows by mitosis into a haploid organism called a
A gametophyte makes haploid gametes by mitosis
Fertilization of gametes results in a diploid sporophyte
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 29Fig. 13-6b
Key
Haploid (n)
Diploid (2n)
n
n
n
n
n
2n
2n
Mitosis
Mitosis
Mitosis
Zygote
Spores
Gametes
MEIOSIS
FERTILIZATION
Diploid
multicellular
organism
(sporophyte)
Haploid multi-
cellular organism
(gametophyte)
(b) Plants and some algae
Слайд 30In most fungi and some protists, the only diploid stage is
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 31Fig. 13-6c
Key
Haploid (n)
Diploid (2n)
Mitosis
Mitosis
Gametes
Zygote
Haploid unicellular or
multicellular organism
MEIOSIS
FERTILIZATION
n
n
n
n
n
2n
(c) Most fungi and some
Слайд 32Depending on the type of life cycle, either haploid or diploid
However, only diploid cells can undergo meiosis
In all three life cycles, the halving and doubling of chromosomes contributes to genetic variation in offspring
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 33Concept 13.3: Meiosis reduces the number of chromosome sets from diploid
Like mitosis, meiosis is preceded by the replication 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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 34The Stages of Meiosis
In the first cell division (meiosis I), homologous
Meiosis I results in two haploid daughter cells with replicated chromosomes; it is called the reductional division
In the second cell division (meiosis II), sister chromatids separate
Meiosis II results in four haploid daughter cells with unreplicated chromosomes; it is called the equational division
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 35Fig. 13-7-1
Interphase
Homologous pair of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated
Sister
chromatids
Diploid cell with
replicated
chromosomes
Слайд 36
Fig. 13-7-2
Interphase
Homologous pair of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated
Sister
chromatids
Diploid cell with
replicated
chromosomes
Meiosis I
Homologous
chromosomes
separate
1
Haploid cells with
replicated chromosomes
Слайд 37
Fig. 13-7-3
Interphase
Homologous pair of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated
Sister
chromatids
Diploid cell with
replicated
chromosomes
Meiosis I
Homologous
chromosomes
separate
1
Haploid cells with
replicated chromosomes
Meiosis II
2
Sister chromatids
separate
Haploid cells with unreplicated chromosomes
Слайд 38Meiosis I is preceded by interphase, in which chromosomes are replicated
The sister chromatids are genetically identical and joined at the centromere
The single centrosome replicates, forming two centrosomes
BioFlix: Meiosis
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 39
Fig. 13-8
Prophase I
Metaphase I
Anaphase I
Telophase I and
Cytokinesis
Prophase II
Metaphase II
Anaphase II
Telophase II
Cytokinesis
Centrosome
(with centriole pair)
Sister
chromatids
Chiasmata
Spindle
Homologous
chromosomes
Fragments
of nuclear
envelope
Centromere
(with kinetochore)
Metaphase
plate
Microtubule
attached to
kinetochore
Sister chromatids
remain attached
Homologous
chromosomes
separate
Cleavage
furrow
Sister chromatids
separate
Haploid daughter cells
forming
Слайд 40Division in meiosis I occurs in four phases:
– Prophase I
– Metaphase I
– Anaphase I
– Telophase
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 41
Metaphase I
Fig. 13-8a
Prophase I
Anaphase I
Telophase I and
Cytokinesis
Centrosome
(with centriole pair)
Sister
chromatids
Chiasmata
Spindle
Homologous
chromosomes
Fragments
of nuclear
envelope
Centromere
(with kinetochore)
Metaphase
plate
Microtubule
attached
kinetochore
Sister chromatids
remain attached
Homologous
chromosomes
separate
Cleavage
furrow
Слайд 42Prophase I
Prophase I typically occupies more than 90% of the time
Chromosomes begin to condense
In synapsis, homologous chromosomes loosely pair up, aligned gene by gene
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 43In crossing over, nonsister chromatids exchange DNA segments
Each pair of chromosomes
Each tetrad usually has one or more chiasmata, X-shaped regions where crossing over occurred
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 44Metaphase I
In metaphase I, tetrads line up at the metaphase plate,
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 45
Fig. 13-8b
Prophase I
Metaphase I
Centrosome
(with centriole pair)
Sister
chromatids
Chiasmata
Spindle
Centromere
(with kinetochore)
Metaphase
plate
Homologous
chromosomes
Fragments
of nuclear
envelope
Microtubule
attached to
kinetochore
Слайд 46Anaphase I
In anaphase I, pairs of homologous chromosomes separate
One chromosome moves
Sister chromatids remain attached at the centromere and move as one unit toward the pole
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 47Telophase I and Cytokinesis
In the beginning of telophase I, each half
Cytokinesis usually occurs simultaneously, forming two haploid daughter cells
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 48In animal cells, a cleavage furrow forms; in plant cells, a
No chromosome replication occurs between the end of meiosis I and the beginning of meiosis II because the chromosomes are already replicated
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 49
Fig. 13-8c
Anaphase I
Telophase I and
Cytokinesis
Sister chromatids
remain attached
Homologous
chromosomes
separate
Cleavage
furrow
Слайд 50Division in meiosis II also occurs in four phases:
– Prophase II
– Metaphase II
– Anaphase
– Telophase II and cytokinesis
Meiosis II is very similar to mitosis
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 51
Fig. 13-8d
Prophase II
Metaphase II
Anaphase II
Telophase II and
Cytokinesis
Sister chromatids
separate
Haploid daughter cells
forming
Слайд 52Prophase II
In prophase II, a spindle apparatus forms
In late prophase II,
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 53Metaphase II
In metaphase II, the sister chromatids are arranged at the
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 55Anaphase II
In anaphase II, the sister chromatids separate
The sister chromatids of
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 56Telophase II and Cytokinesis
In telophase II, the chromosomes arrive at opposite
Nuclei form, and the chromosomes begin decondensing
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 57Cytokinesis separates the cytoplasm
At the end of meiosis, there are four
Each daughter cell is genetically distinct from the others and from the parent cell
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 58
Fig. 13-8f
Anaphase II
Telephase II and
Cytokinesis
Sister chromatids
separate
Haploid daughter cells
forming
Слайд 59A Comparison of Mitosis and Meiosis
Mitosis conserves the number of chromosome
Meiosis reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell
The mechanism for separating sister chromatids is virtually identical in meiosis II and mitosis
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 60Fig. 13-9
MITOSIS
MEIOSIS
MEIOSIS I
Prophase I
Chiasma
Homologous
chromosome
pair
Chromosome
replication
Parent cell
2n = 6
Chromosome
replication
Replicated chromosome
Prophase
Metaphase
Metaphase I
Anaphase I
Telophase I
Haploid
n
Daughter
cells of
meiosis I
Anaphase
Telophase
2n
2n
Daughter cells
of mitosis
n
n
n
n
MEIOSIS II
Daughter cells of meiosis II
SUMMARY
Meiosis
Occurs during interphase before meiosis I begins
Two, each including prophase, metaphase, anaphase, and
telophase
Occurs during prophase I along with crossing over
between nonsister chromatids; resulting chiasmata
hold pairs together due to sister chromatid cohesion
Four, each haploid (n), containing half as many chromosomes
as the parent cell; genetically different from the parent
cell and from each other
Produces gametes; reduces number of chromosomes by half
and introduces genetic variability amoung the gametes
Mitosis
Occurs during interphase before
mitosis begins
One, including prophase, metaphase,
anahase, and telophase
Does not occur
Two, each diploid (2n) and genetically
identical to the parent cell
Enables multicellular adult to arise from
zygote; produces cells for growth, repair,
and, in some species, asexual reproduction
Property
DNA
replication
Number of
divisions
Synapsis of
homologous
chromosomes
Number of
daughter cells
and genetic
composition
Role in the
animal body
Слайд 61Fig. 13-9a
MITOSIS
MEIOSIS
MEIOSIS I
Prophase I
Chiasma
Chromosome
replication
Homologous
chromosome
pair
Chromosome
replication
2n = 6
Parent cell
Prophase
Replicated chromosome
Metaphase
Metaphase I
Anaphase I
Telophase I
Haploid
Daughter
cells of
meiosis I
MEIOSIS II
Daughter cells of meiosis II
n
n
n
n
2n
2n
Daughter cells
of mitosis
Anaphase
Telophase
Слайд 62Fig. 13-9b
SUMMARY
Meiosis
Mitosis
Property
DNA
replication
Number of
divisions
Occurs during interphase before
mitosis begins
One, including prophase, metaphase,
anaphase, and
Synapsis of
homologous
chromosomes
Does not occur
Number of
daughter cells
and genetic
composition
Two, each diploid (2n) and genetically
identical to the parent cell
Role in the
animal body
Enables multicellular adult to arise from
zygote; produces cells for growth, repair,
and, in some species, asexual reproduction
Occurs during interphase before meiosis I begins
Two, each including prophase, metaphase, anaphase, and
telophase
Occurs during prophase I along with crossing over
between nonsister chromatids; resulting chiasmata
hold pairs together due to sister chromatid cohesion
Four, each haploid (n), containing half as many chromosomes
as the parent cell; genetically different from the parent
cell and from each other
Produces gametes; reduces number of chromosomes by half
and introduces genetic variability among the gametes
Слайд 63Three events are unique to meiosis, and all three occur in
– Synapsis and crossing over in prophase I: Homologous chromosomes physically connect and exchange genetic information
– At the metaphase plate, there are paired homologous chromosomes (tetrads), instead of individual replicated chromosomes
– At anaphase I, it is homologous chromosomes, instead of sister chromatids, that separate
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 64Sister chromatid cohesion allows sister chromatids of a single chromosome to
Protein complexes called cohesins are responsible for this 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)
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 65
Fig. 13-10
EXPERIMENT
RESULTS
Shugoshin+ (normal)+
Spore case
Fluorescent label
Metaphase I
Shugoshin–
Anaphase I
Metaphase II
Anaphase II
Mature
spores
OR
Spore
Two of three
ments of labeled chromosomes
Shugoshin+
Shugoshin–
Spore cases (%)
100
80
60
40
20
0
?
?
?
?
?
?
?
?
Слайд 66
Fig. 13-10a
EXPERIMENT
Shugoshin+ (normal)
Spore case
Fluorescent label
Metaphase I
Anaphase I
Metaphase II
Anaphase II
Mature
spores
Spore
OR
Two of three
ments of labeled chromosomes
Shugoshin–
?
?
?
?
?
?
?
?
Слайд 68Concept 13.4: Genetic variation produced in sexual life cycles contributes to
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 69Origins of Genetic Variation Among Offspring
The behavior of chromosomes during meiosis
Three mechanisms contribute to genetic variation:
Independent assortment of chromosomes
Crossing over
Random fertilization
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 70Independent Assortment of Chromosomes
Homologous pairs of chromosomes orient randomly at metaphase
In independent assortment, each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 71The number of combinations possible when chromosomes assort independently into gametes
For humans (n = 23), there are more than 8 million (223) possible combinations of chromosomes
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 72Fig. 13-11-1
Possibility 1
Possibility 2
Two equally probable
arrangements of
chromosomes at
metaphase I
Слайд 73Fig. 13-11-2
Possibility 1
Possibility 2
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Слайд 74Fig. 13-11-3
Possibility 1
Possibility 2
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Daughter
cells
Combination 1
Combination
Combination 3
Combination 4
Слайд 75Crossing Over
Crossing over produces recombinant chromosomes, which combine genes inherited from
Crossing over begins very early in prophase I, as homologous chromosomes pair up gene by gene
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Слайд 76In crossing over, homologous portions of two nonsister chromatids trade places
Crossing
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Слайд 77Fig. 13-12-1
Prophase I
of meiosis
Pair of
homologs
Nonsister
chromatids
held together
during synapsis
Слайд 78Fig. 13-12-2
Prophase I
of meiosis
Pair of
homologs
Nonsister
chromatids
held together
during synapsis
Chiasma
Centromere
TEM
Слайд 79Fig. 13-12-3
Prophase I
of meiosis
Pair of
homologs
Nonsister
chromatids
held together
during synapsis
Chiasma
Centromere
Anaphase I
TEM
Слайд 80Fig. 13-12-4
Prophase I
of meiosis
Pair of
homologs
Nonsister
chromatids
held together
during synapsis
Chiasma
Centromere
Anaphase I
Anaphase II
TEM
Слайд 81Fig. 13-12-5
Prophase I
of meiosis
Pair of
homologs
Nonsister
chromatids
held together
during synapsis
Chiasma
Centromere
Anaphase I
Anaphase II
Daughter
cells
Recombinant chromosomes
TEM
Слайд 82Random Fertilization
Random fertilization adds to genetic variation because any sperm can
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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Слайд 83Crossing over adds even more variation
Each zygote has a unique genetic
Animation: Genetic Variation
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Слайд 84The Evolutionary Significance of Genetic Variation Within Populations
Natural selection results in
Sexual reproduction contributes to the genetic variation in a population, which originates from mutations
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Слайд 85Fig. 13-UN1
Prophase I: Each homologous pair undergoes
synapsis and crossing over between
chromatids.
Metaphase I: Chromosomes line up as homolo-
gous pairs on the metaphase plate.
Anaphase I: Homologs separate from each other;
sister chromatids remain joined at the centromere.
Слайд 89You should now be able to:
Distinguish between the following terms: somatic
Describe the events that characterize each phase of meiosis
Describe three events that occur during meiosis I but not mitosis
Name and explain the three events that contribute to genetic variation in sexually reproducing organisms
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