bio3 0910 lec4 meiosis
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MeiosisBiology 3 Kawashima
Philippine Science High SchoolSY 2009-2010
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Homologous chromosomes condense at prophase I
• Homologous chromosomes pair along their lengths, aligned gene by gene
• Synaptonemal complex forms between homologues, holding them together along their lengths
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Homologous chromosomes condense at prophase I
• Synaptonemal complex disassembles in late prophase I, and each chromosome pair become visible as a tetrad
• A tetrad is a group of four chromotids
• Each tetrad has one or more chiasmata, cris-crossed regions where crossing-over has occured
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Tetrads align on the metaphase plate at metaphase I
• Chiasmata are still intact• One chromosome of
each pair face the pole• Chromatids of
homologous chromosomes are attached to kinetochore microtubules from one pole
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Homologous chromosomes separate at anaphase I
• Sister chromatids remain attached at the centromere
• Sister chromatids move towards the same pole
• Homologous chromosomes, each composed of two sister chromatids, move to opposite poles
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Each half has a complete haploid set of chromosomes at telophase I
• Each chromosome is still composed of two sister chromatids
• Cytokenesis begins to form two daughter cells, each with a haploid set of chromosomes
• No chromosome doubling occurs between telophase I and prophase II, as they have already been replicated
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Meiosis I
• Homologous chromosomes condense at prophase I
• Tetrads align on the metaphase plate at metaphase I
• Homologous chromosomes separate at anaphase I
• Each half has a complete haploid set of chromosomes at telophase I
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