Meiosis and Sexual Life Cycles

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Chapter 13 Meiosis and Sexual Life Cycles
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Fig. 13-1
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The Birds and the Bees
Asexual vs. Sexual reproduction
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Fig. 13-2a
0.5 mm
Parent
Bud
(a) Hydra
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(No Transcript)
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Chromosome arrangement

• Somatic cells typical body cells
• 46 chromosomes in 23 pairs (humans)
• Each pair is called homologous chromosomes
• Gametes sex cells
• 23 chromosomes

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Homologous chromosomes

• 22 of the pairs (autosomes) are true homologues
• One of each came from mom and dad
• Identical in length and type of genes carried
• Genes on each are slightly different
• Sex chromosomes (23rd pair) dont match up
  exactly (X vs Y)

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Fig. 13-3b
KARYOTYPE
5 µm
Pair of homologous replicated chromosomes
Centromere
Sister chromatids
Metaphase chromosome
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Fig. 13-4
Key
Maternal set of chromosomes (n 3)
2n 6
Paternal set of chromosomes (n 3)
Two sister chromatids of one replicated chromosome
Centromere
Two nonsister chromatids in a homologous pair
Pair of homologous chromosomes (one from each set)
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Fig. 13-5
Key
Haploid gametes (n 23)
Haploid (n)
Egg (n)
Diploid (2n)
Sperm (n)
MEIOSIS
FERTILIZATION
Ovary
Testis
Diploid zygote (2n 46)
Mitosis and development
Multicellular diploid adults (2n 46)
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Fig. 13-6
Key
Haploid (n)
Haploid unicellular or multicellular organism
Haploid multi- cellular organism (gametophyte)
Diploid (2n)
Gametes
n
n
Mitosis
Mitosis
Mitosis
Mitosis
n
n
n
n
n
n
n
n
Spores
FERTILIZATION
n
MEIOSIS
n
Gametes
Gametes
n
MEIOSIS
FERTILIZATION
Zygote
MEIOSIS
FERTILIZATION
2n
2n
2n
2n
Diploid multicellular organism
Zygote
Diploid multicellular organism (sporophyte)
2n
Mitosis
Mitosis
Zygote
(a) Animals
(b) Plants and some algae
(c) Most fungi and some protists
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Meiosis

• Produces haploid cells
• Results in four daughter cells
• All are haploid
• All are genetically unique from each other and
  from the parent
• DNA replicated before meiosis begins
• Two stages
• Meiosis I separates homologous chromosomes
• Meiosis II separates sister chromatids

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Fig. 13-7-1
Interphase
Homologous pair of chromosomes in diploid parent
cell
Chromosomes replicate
Homologous pair of replicated chromosomes
Sister chromatids
Diploid cell with replicated chromosomes
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Fig. 13-7-2
Interphase
Homologous pair of chromosomes in diploid parent
cell
Chromosomes replicate
Homologous pair of replicated chromosomes
Sister chromatids
Diploid cell with replicated chromosomes
Meiosis I
Homologous chromosomes separate
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Haploid cells with replicated chromosomes
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Fig. 13-7-3
Interphase
Homologous pair of chromosomes in diploid parent
cell
Chromosomes replicate
Homologous pair of replicated chromosomes
Sister chromatids
Diploid cell with replicated chromosomes
Meiosis I
Homologous chromosomes separate
1
Haploid cells with replicated chromosomes
Meiosis II
Sister chromatids separate
2
Haploid cells with unreplicated chromosomes
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Fig. 13-8a
Telophase I and Cytokinesis
Metaphase I
Prophase I
Anaphase I
Centrosome (with centriole pair)
Sister chromatids remain attached
Centromere (with kinetochore)
Sister chromatids
Chiasmata
Spindle
Metaphase plate
Cleavage furrow
Homologous chromosomes separate
Homologous chromosomes
Microtubule attached to kinetochore
Fragments of nuclear envelope
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Fig. 13-8d
Telophase II and Cytokinesis
Prophase II
Metaphase II
Anaphase II
Sister chromatids separate
Haploid daughter cells forming
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Fig. 13-9a
MITOSIS
MEIOSIS
MEIOSIS I
Chiasma
Parent cell
Chromosome replication
Chromosome replication
Prophase I
Prophase
Homologous chromosome pair
2n 6
Replicated chromosome
Metaphase I
Metaphase
Anaphase I
Anaphase Telophase
Telophase I
Haploid n 3
Daughter cells of meiosis I
MEIOSIS II
2n
2n
Daughter cells of mitosis
n
n
n
n
Daughter cells of meiosis II
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Fig. 13-9b
SUMMARY
Meiosis
Mitosis
Property
DNA replication
Occurs during interphase before mitosis begins
Occurs during interphase before meiosis I begins
Number of divisions
One, including prophase, metaphase, anaphase, and
telophase
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
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
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 chromosomes
by half and introduces genetic variability among
the gametes
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Sexual Reproduction leads to genetic variation!

• 3 process that contribute to variation
• Independent assortment of chromosomes
• Crossing over
• Random fertilization

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Fig. 13-11-1
Possibility 2
Possibility 1
Two equally probable arrangements of chromosomes
at metaphase I
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Fig. 13-11-2
Possibility 2
Possibility 1
Two equally probable arrangements of chromosomes
at metaphase I
Metaphase II
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Fig. 13-11-3
Possibility 2
Possibility 1
Two equally probable arrangements of chromosomes
at metaphase I
Metaphase II
Daughter cells
Combination 1
Combination 2
Combination 3
Combination 4
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Sexual Reproduction leads to genetic variation!

• 3 process that contribute to variation
• Independent assortment of chromosomes
• Crossing over
• Random fertilization

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Fig. 13-12-1
Prophase I of meiosis
Nonsister chromatids held together during synapsis
Pair of homologs
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Fig. 13-12-2
Prophase I of meiosis
Nonsister chromatids held together during synapsis
Pair of homologs
Chiasma
Centromere
TEM
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Fig. 13-12-3
Prophase I of meiosis
Nonsister chromatids held together during synapsis
Pair of homologs
Chiasma
Centromere
TEM
Anaphase I
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Fig. 13-12-4
Prophase I of meiosis
Nonsister chromatids held together during synapsis
Pair of homologs
Chiasma
Centromere
TEM
Anaphase I
Anaphase II
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Fig. 13-12-5
Prophase I of meiosis
Nonsister chromatids held together during synapsis
Pair of homologs
Chiasma
Centromere
TEM
Anaphase I
Anaphase II
Daughter cells
Recombinant chromosomes
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Sexual Reproduction leads to genetic variation!

• 3 process that contribute to variation
• Independent assortment of chromosomes
• Crossing over
• Random fertilization

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Darwin vs. Mendel