Ch 13-15 meiosis struc

Ch 13-15 meiosis struc - What we will cover? 1. What does...

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What we will cover? 1. What does meiosis do 1. What are haploid cells used for 1. Meiosis I is the reductional division 1. Meiosis II separates homologous chromosomes 1. Differences between meiosis and mitosis
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1. What does meiosis do
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Meiosis reduces diploid to haploid -many steps resemble steps in mitosis -preceded by replication of chromosomes -followed by two divisions 1. meiosis I 2. meiosis II -result in four daughter cells with half the chromosome number
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What is a diploid set of chromosomes - diploid cells have two sets of the same chromosome (2n) -one set inherited from maternal other from parental -each copy of chromosome has same genes -different versions of genes on each chromosome
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-haploid set one of each homologous chromosomes (n) -when condensed DNA has replicated -homologous chromosomes have sister chromatid ex humans 46 chromosomes diploid 2N -haploid 23 sets of chromosomes N
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How to visualize homologous chromosomes -karyotype -cells stimulated to enter mitosis -arrested at metaphase -image taken of condensed chromosomes -homologous chromosomes arranged
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2. What are haploid cells used for
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Why make haploid cells? - sexual reproduction utilizes the fusion of gametes from maternal and paternal -fusing two cells with 46 chromosomes would increase to 92 -next generation would double again -need to maintain same number -reduce to half- fusion of gametes returns to 46
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How are haploid cells formed? -chromosomes of a diploid cell are duplicated -each duplicated chromatid is separated to a new daughter cell -homologues have same genes -may be different version of gene
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3. Meiosis I is the reductional division
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Details of meiosis I - interpahse I - chromosomes replicate - prophase I - condensation -homologous chromosomes pair - crossing over - recombination of chromosomes
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- metaphase I -fully condensed chromosomes -line up as tetrads at metaphase plate -each pair attached to one microtubule -pairs line up randomly - anaphase I - pairs of chromosomes pulled towards centrosomes -move towards opposite poles -sister chromatids remain attached
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telophase I and cytokinesis - -chromosomes have moved to opposite poles -some species chromosomes decondense and nuclear membrane reforms -two daughter cells form by cytokinesis - cell is now haploid -still have duplicated chromosomes -separate out in second phase of meiosis
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4. Meiosis II separates homologous chromosomes
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Second phase of meiosis separates sister chromatids -no replication occurs before this division -no interphase occurs between I and II -begins with prophase II - nuclear membrane disperses -chromosomes condense -spindle apparatus reforms -chromosomes begin to move towards metaphase plate -no crossing over at this stage
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- metaphase II - chromosomes are positioned on the metaphase plate -kinetochores of sister chromosomes are attached to microtubules of opposite poles anaphase II - centromeres of sister chromatids separate -individual chromatids move to opposite poles
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- -nuclear membrane reforms -chromosomes decondense -four daughter cells form with single copy of haploid chromosomes -each cell genetically distinct
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This note was uploaded on 04/07/2008 for the course BIO Gen Bio taught by Professor Wallace during the Spring '08 term at Clarkson University .

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Ch 13-15 meiosis struc - What we will cover? 1. What does...

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