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Cell Division
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Meiosis Meiosis occurs in sexual
reproduction when a diploid germ cell produces four haploid daughter cells that can mature to become gametes (sperm or egg).
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Meiosis
Goal: reduce genetic material by half
Why? n (mom) + n (dad) = 2n (offspring)from mom from dad child
meiosis reducesgenetic content
toomuch!
Just right!
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Meiosis: 2 part cell division
Homologous Chromosomes pairs separate
Sister chromatidsseparate
Result: one copy of each numbered chromosome in a gamete.
Haploid
Diploid
Meiosis I Meiosis II
Haploid
2n
nn
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Meiosis I
Prophase I(early)
(diploid)
Prophase I(late)
(diploid)
Metaphase I(diploid)
Anaphase I(diploid)
Telophase I(diploid)
Nucleus Spindlefibers
Nuclearenvelope
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Prophase I Early
Early prophase Chromosomes
condenseSpindle forms
Nuclear envelope breaks apart
.
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Prophase I Late
Late prophase Chromatids pair (synapse)
Crossing over occurs between chromatids of the homologous chromosome pair
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Metaphase I
Homologous chromosome pairs line up on the cell’s equator
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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 reforms
Spindle disappears.
Cytokinesis divides cell into two
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Meiosis II
End product of meiosis is Each Sex cell /gamete has :1 copy of each chromosome1 copy of each gene segment
Sister chromatids have carry different genetic information due to crossing over
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Meiosis II
Prophase II(haploid)
Metaphase II(haploid)
Anaphase II(haploid)
Telophase II(haploid)
Four Non-identical
haploid daughter cells
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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
•Not the same genes on each chromosome
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“Putting It All Together” - Fertilization
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What Meiosis is About
Meiosis allows the creation of unique individuals through sexual reproduction.
Meiosis Video Link
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Meiosis Video Link #1
Meiosis Video Link #2
Meiosis Video Link#3
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2 diploid 4 haploid Crossing over between nonsister
chromatids Reduction divisiion Increases genetic variability vs. clones Meiosis 1 Homologous chrom separate Meiosis 2 Sister chromatids separate
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Mitosis Meiosis
Number of divisions 1 2
Number of daughter cells made through
process
2 4
Are the new cells Genetically
identical?Yes No
# of Chromosomes
compared to parent cell
Same as parent Half of parent
What cell go thru this
division processSomatic cells Sex cells
When do cells got thru this
division processThroughout life At sexual maturity
Role Growth and repair Sexual reproduction
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MITOSIS MEIOSIS
Occurs in somatic (body) cells Occurs only in gonads (sex organs: ovary/testes)
Produces cells for repair,maintenance, growth, asexual reproduction
Only produces gametes (sex cells: egg/sperm)
Results in identical diploid (2n) daughter cells
Reduction division results in haploid (n) cells
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Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene.