Download Bell Work: What is the difference between a haploid and diploid cell?

meiosisnotes.notebook
November 14, 2013
Thursday, November 21 Bell Work:
What is the difference between a haploid and diploid cell?
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meiosisnotes.notebook
November 14, 2013
Review Mitosis:
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meiosisnotes.notebook
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Prophase I
­DNA coils into chromosomes
­Spindle fibers form
­Nuclear membrane breaks down
­Centrioles move to opposite sides of the cell.
­Crossing over occurs here.
­Homologous chromosomes line up gene to gene in a four­part structure called a tetrad. ­Tetrad is made up of 2 homologous chromosomes, with 2 sister chromatids.
­Sex chromosomes also pair up with one another
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meiosisnotes.notebook
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Crossing Over­ The exchange of chromosome segments between homologous chromosomes during prophase I of meiosis.
­Exchange of genetic material creates more genetic diversity.
­Results in a new combination of alleles, called genetic recombination.
­Can occur at any location on a chromosome and in several locations at the same time.
Draw a detailed picture using colored pencils to show crossing over occuring. pg 190
In humans approximately 2­3 crossovers for each pair of homologous chromosomes.
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meiosisnotes.notebook
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Linked Genes or (genetic linkage)
­genes that are close together on the same chromosome are more likely to be inherited together (linked together)
­the farther apart two genes are located, the more likely they are to be separated when crossing over.
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Metaphase I
­Centromere attaches to spindle fibers
­Homologous chromosomes are lined up side by side in the middle as tetrads. **Remember: In mitosis they were a single file line**
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meiosisnotes.notebook
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Anaphase I:
­Homologous chromosomes separate and move to opposite ends of the cell.
­Centromere does NOT split, sister chromatids stay together.
­Ensures that each new cell will only have 1 chromosome from each homologous pair.
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meiosisnotes.notebook
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Telophase I:
­Nuclear membrane forms again.
­Spindle fibers break down
­Cytoplasm divides
­We end up with 2 cells with a unique combination of 23 duplicated chromosomes coming from both parents.
Note: Still contains doubled chromosomes. Therefore, a second cell division is necessary to separate the doubled chromsomes
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Meiosis II: Exactly like mitosis. It divides sister chromatids resulting in undoubled chromosomes. The process described below relates to both cells.
Note: DNA is NOT copied again between the two stages.
Directions: Use pages 174­175 to describe what occurs during each phase and complete a detailed picture of each stage.
Prophase II
­ The nuclear membrane breaks down
­ Centrioles move to opposite sides of the cell.
­Spindle fibers form
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meiosisnotes.notebook
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Metaphase II
­Spindle fibers align the 23 chromosomes at the cell equator (in the middle).
Anaphase II
­Sister chromatids are pulled apart from each other and move to opposite sides of the cell.
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meiosisnotes.notebook
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Telophase II:
­Nuclear membranes form around each set of chromosomes at opposite ends of the cell. ­Spindle fibers break apart.
­cell undergoes cytokinesis
END RESULT OF MEIOSIS
­Four haploid cells with a combination of chromosomes from mom and dad.
­Haploid cells become gametes transferring the genes they contain to the offspring.
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