MEIOSIS - Mrs. MoodyMEIOSIS Each phase (PMAT) happens twice End with 4 daughter cells Each cell in...
Transcript of MEIOSIS - Mrs. MoodyMEIOSIS Each phase (PMAT) happens twice End with 4 daughter cells Each cell in...
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MEIOSIS
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Why don’t siblings look exactly alike if
they have the same parents?
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The Process of
Meiosis
Meiosis is divided
into two phases:
Meiosis I and
Meiosis II
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Prophase I
Early prophase
Chromatids pair. Crossing over occurs.
Late prophase
Chromosomes condense.Spindle forms.
Nuclear envelope fragments.
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Crossing Over in Meiosis I
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Metaphase I
Chromatid pairs alignalong the equator of the cell.
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Anaphase I
Chromosomes separate andmove to opposite poles.
Sister chromatids remain Attached at their centromeres.
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Telophase I
Nuclear envelopes reassemble.
Spindle disappears.
Cytokinesis divides cell into two.
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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 separateand move to opposite poles.
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Telophase II
Nuclear envelope assembles.
Chromosomes unravel.
Spindle disappears.
Cytokinesis divides cell into two.
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Results of meiosis
• Four haploid cells
• One copy of each chromosome •animation
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MEIOSIS
Each phase (PMAT) happens twice
End with 4 daughter cells
Each cell in the end (gamete) only has half the number of
chromosomes (Haploid)
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Terms to know
Diploid –
Haploid –
Chromosome -
Sister Chromatid
Gametes
Fertilization
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Diploid versus Haploid
Diploid cells have two of each kind of chromosome. 2n
Haploid cells have only one of each kind of chromosome. N
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Number of Chromosomes in Common Organisms
Organism Body Cell (2n)
Diploid
Gamete (n)
haploid
Fruit Fly 8 4
Garden Pea 7
Corn 20
Leopard Frog 13
Apple 34
Human 23
Chimpanzee 48
Dog 39
Adder’s tounge Fern 1260
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Terms to know
Diploid –
Haploid –
Chromosome -
Sister Chromatid
Gametes
Fertilization
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“Putting It All Together” - Fertilization
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meiosis
Where???
Only in REPRODUCTIVE ORGANS
Testes, Ovaries, flower (plants)
WHY??
Produces cells required for sexual reproduction
Gametes cells
Sperm, egg
Pollen, Ovule
Final Product??
4 Haploid cells that are different
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Back to our original question...
Why don’t siblings look
exactly alike if they have
the same parents?
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Meiosis Creates Genetic Variation
Crossing Over - creates new genetic combinations
Random Alignment - Chromosomes line up randomly during Metaphase I
so all chromosomes from mother or father do not end up in same gamete
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Crossing Over in Meiosis I
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Meiosis Creates Genetic Variation
Crossing Over - creates new genetic combinations
Random Alignment - Chromosomes line up randomly during Metaphase I
so all chromosomes from mother or father do not end up in same gamete