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Meiosis

Meiosis . Section 11-4 Pages 275-278. Meiosis. Meiosis—the process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. Chromosome Number. Human—46 chromosomes 23 from male parent

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Meiosis

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  1. Meiosis Section 11-4 Pages 275-278

  2. Meiosis • Meiosis—the process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell

  3. Chromosome Number • Human—46 chromosomes • 23 from male parent • 23 from female parent

  4. Homologous—chromosomes that each have a corresponding chromosome from the opposite-sex parent • Diploid—cells that have both sets of homologous chromosomes (2N) • For humans diploid number is 46 (2N=46)

  5. Chromosome Number • Gametes (sex cells) contain only a single set of chromosomes • Haploid—cells (gametes) that contain only a single set of chromosomes (N) • For humans haploid number is 23 (N=23) • Will you find haploid cells within the skin on your arm? Why or why not?

  6. Phases of Meiosis I • Prior to meiosis I each chromosome is replicated (DNA replication) • Meiosis I looks very similar to mitosis • Prophase of meiosis I—each chromosome pairs with its corresponding homologous chromosome to from a tetrad • 4 chromatids to a tetrad

  7. Meiosis I • Crossing-over—portions of chromatids are exchanged while in tetrads • Metaphase I—tetrads line up across middle of cell • Anaphase I—homologous chromosomes are seperated • Because of separation of homologous chromosomes new daughter cell has only one copy of each chromosome

  8. Meiosis II • Two cells produced by meiosis I enter another meiotic division • No replication takes place • Each cell contains 2 sister chromatids • Metaphase II—chromosomes line up in the center of each cell • Anaphase II—the paired chromatids separate • Each of the 4 daughter cells produced in meiosis II contain the haploid number of chromosomes – in people N=23

  9. Comparing Mitosis and Meiosis • Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid cells • Mitosis—two diploid (2N) daughter cells • Meiosis—four haploid (N) cells

  10. Picture Credits • http://employees.csbsju.edu/hjakubowski/classes/ch331/dna/chromosomes.gif • http://www.microscopix.co.uk/chromosomes/16306.gif • http://www.emc.maricopa.edu/faculty/farabee/biobk/meiosisover.jpg • www.distance.stcc.edu/.../celldivision/tetrad.gif • http://www.cancerquest.emory.edu/images/mitosis-cycai.gif • http://www.palaeos.com/Fungi/Lists/Glossary/Images/Meiosis.gif

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