Cell Division Meiosis Cell Division Meiosis Abnormal Meiosis.
Section 8-3 Meiosis
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Transcript of Section 8-3 Meiosis
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Section 8-3 Meiosis
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Obj 9: List and describe the phases of meiosis
Meiosis I: Preceded by copying of DNA in interphase
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Prophase I
Homologous chromosomes pair each pair = tetrad (4 chromatids) Crossing-over may occur
Chromatids twist around each other & parts are exchanged (genetic recombination)
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Metaphase I
tetrads line up
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Anaphase I
chromosomes move to opposite poles independent
assortment - random separation of chromosomes, resulting in genetic variation
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Independent assortment http://10.20.0.2/videos/pmp/videos/wm
/1MB/8VH0457G_1Mb.wmv
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Telophase I
chromosomes reach opposite poles
cytokinesis forms 2 cells
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Meiosis II
Not preceded by copying of DNA Occurs in both cells Same 4 phases - prophase II,
metaphase II, etc.
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Meiosis II
Difference: In anaphase II,
chromatids separate (not chromosomes)
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Obj 10: Compare the products of mitosis with those of meiosis
Both from a 2n parent cell:
Mitosis produces 2 diploid (2n) daughter cells
Meiosis produces 4 haploid (1n) gametes
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Meiosis
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Obj 11: Explain crossing-over and how it contributes to the production of unique individuals
During pairing up, chromosomes exchange DNA results in new
(unique) genetic combinations
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Obj 12: Summarize the major characteristics of spermatogenesis and oogenesis
Spermatogenesis: Cytoplasm
divides evenly and produces 4 haploid cells
Spermatids grow flagella and are oval
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Oogenesis: Cytoplasm divides
unevenly Egg receives
majority of cytoplasm
Polar bodies receive little cytoplasm will die and are
absorbed