Meiosis

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Section 11.4

• Meiosis

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A) Stages of Meiosis

• -Final product will be 4 haploid cells
• -2 stage process
• a) Meiosis I
• b) Meiosis II

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Meiosis 2 divisions
Sister chromatids separate
Homologs separate
Result one copy of each chromosome in a gamete.
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A) Stages of Meiosis

• Interphase- replicate DNA
• G1
• S
• G2

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A) Stages of Meiosis

• 1) Meiosis I
• a) Prophase (same as Mitosis w/ extra)
• 1. Synapsis
• 2. Crossing over exchange pieces of _________
  btwn homologous pair
• a) genetic recombination exchange of

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a) Prophase I
Early prophase Homologs pair. Crossing over
occurs.
Late prophase Chromosomes condense. Spindle
forms. Nuclear envelope fragments.
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Recombination (crossing over)

• Occurs in prophase of meiosis I
• Generates diversity

a
A
a
A
B
b
B
b
c
c
C
C
D
D
d
d
E
E
e
e
Letters denote genes Case denotes alleles
F
F
f
f

• Creates chromosomes with new combinations of
  alleles for genes A to F.

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Chiasmata
Crossing over or recombination events create
chiasmata.
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b) Metaphase I
1. Homolog pairs align along the equator of the
cell 2. Sister Chromatids facing opposite poles
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c) Anaphase II
Homologs separate and move to opposite
poles. Sister chromatids remain Attached at
their centromeres
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A) Stages of Meiosis

• Metaphase I-
• 1. __________ line up in the middle of the cell
• Anaphase I-
• 1.
• 2. independent assortment random separation of
  homologues ________________

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A) Stages of Meiosis

• d) Telophase I-
• 1. chromosomes reach poles
• 2. _____________ takes place
• 3. 2 new haploid cells created ( 2 copies of
  chromosomes in each cell)

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Telophase I
Nuclear envelopes reassemble. Spindle
disappears. Cytokinesis divides cell into two.
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Meiosis I reduction division
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A) Stages of Meiosis

• 2) Meiosis II
• a) Prophase II
• 1. spindle fibers appear
• b) Metaphase II
• 1. chromosomes align in middle of cell
• c) Anaphase II
• 1. Sister chromatids move toward poles
• d) Telophase II
• 1. nuclear envelope appears cytokinesis takes
  place

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Prophase II
Nuclear envelope fragments. Spindle forms.
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Metaphase II
Chromosomes align along equator of cell.
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Anaphase II
Sister chromatids separate and move to opposite
poles.
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Telophase II
Nuclear envelope assembles. Chromosomes
decondense. Spindle disappears. Cytokinesis
divides cell into two.
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A) Stages of Meiosis

• Results of Meiosis
• ______ Haploid cells are created
• Contains ______ the of chromosomes as original
  cell
• _________ variation

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Mitosis Meiosis
Number of divisions 1 2
Number of daughter cells 2 4
Genetically identical? Yes No
Chromosome Same as parent Half of parent
When Throughout life At sexual maturity
Role Growth and repair Sexual reproduction
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B) Formation of Gametes

• Animal cell meiosis occurs in reproductive
  organs
• a) Ex __________________
• Spermatogenesis production of _______
• Oogenesis production of ________
• a) Polar bodies remaining cells from meiosis

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Sperm and Egg
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C) Asexual and Sexual Reproduction

• Asexual Reproduction reproduction of offspring
  from 1 parent
• a) Ex _____________
• Sexual Reproduction reproduction of offspring by
  a sex cell from each parent