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Meiosis

Meiosis. Formation of Sex Cells to Transfer Genetic Information to the Next Generation. Diploid number of chromosomes, two full sets. Haploid number of chromosomes, one full set. Nuclear division retaining the original chromosome number. Mitosis and Meiosis in the Human Life Cycle.

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Meiosis

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  1. Meiosis Formation of Sex Cells to Transfer Genetic Information to the Next Generation

  2. Diploid number of chromosomes, two full sets Haploid number of chromosomes, one full set Nuclear divisionretaining the original chromosome number Mitosis and Meiosis in the Human Life Cycle Nuclear divisionreducing the chromosome number,leading to sperm or eggs

  3. InterphaseMitosisCytokinesis InterphaseMeiosisCytokinesis Mitosis and Meiosis Human Cell with 46 chromosomes (DIPLOID) Human Cell with 46 chromosomes (DIPLOID) 2 Genetically-Identical Human Cells each with 46 chromosomes (DIPLOID) 4 Genetically-Different Human Cells each with 23 chromosomes (HAPLOID)

  4. Homologous Chromosome Pairs • Diploid cells have pairs of chromosomes • Each homologous chromosome pair is genetically matched so that the genes are arranged in the same order • Meiosis distributes members of each pair to separate nuclei Humans have 1 pair of sex chromosomes and 22 pairs of autosomes

  5. Meiosis G2 synthesis of proteins and assembly of components for division cytokinesis cytokinesis S G1 cytoplasm doubles, including organelles chromosomes duplicate Cell Cycle With Meiosis Interphase includes G1 = growth phase 1 S = synthesis phase G2 = growth phase 2 Meiosis I Meiosis II Meiosis includes two chromosomal divisionsMeiosis IMeiosis II Cytokinesis = division of cytoplasmic contents Interphase

  6. When does chromosomal division occur? When do the cytoplasmic contents double? When does chromosome duplication occur? G1 phase S phase G2 phase Meiosis I and II Applying Your Knowledge

  7. Equational Division: Separation of sister chromatids, no change in chromosome number Reduction Division: Separation of homologous chromosomes, reducing the chromosome number to haploid Meiosis Involves Two Chromosomal Divisions

  8. Homologous Chromosome Pair Duplicated chromosomes joined at their centromeres Nonsister Chromatids are joined to differentcentromeres Duplicated Chromosomes in Early Meiosis Centromere = constricted region

  9. Prophase I of Meiosis I • Chromosomes thicken • Genetic exchange occurs between nonsister chromatids through crossing-over

  10. Spindle fiber Metaphase I of Meiosis I • Homologous pairs line up at the cell equator • Spindle fibers attached to centromeres cause chromosomal movement

  11. Anaphase I and Telophase I of Meiosis I Anaphase I • Members of homologous pair separate and are pulled to opposite poles of the cell Telophase I • Chromosomes reach opposite poles + cytokinesis Cytokinesis • Cytoplasm divides into two separate cells Daughter cells are haploid with duplicated chromosomes

  12. Prophase II and Metaphase II of Meiosis II Prophase II • Chromosomes thicken Metaphase II • Chromosomes line up at cell equator

  13. Anaphase II and Telophase II of Meiosis II Anaphase II • Sister Chromatids separate and move to opposite poles Telophase II • Chromosomes have reached opposite poles + cytokinesis Cytokinesis • Cytoplasm divides into separate cells Daughter cells are haploidand have genetic differences

  14. When do sister chromatids separate? When does crossing-over occur? When do homologous pairs line up at the cell equator? Prophase I Metaphase I Anaphase I Metaphase II Anaphase II Applying Your Knowledge

  15. Sperm formation • Equal divisions of cytoplasm • Four functional products per meiosis • Egg formation • Unequal divisions of cytoplasm • Small polar bodies formed • One functional product per meiosis Fertilization occurs after Meiosis I and stimulates Meiosis II

  16. Comparing Mitosis and Meiosis

  17. Comparing Mitosis and Meiosis Diploid Diploid Diploid Haploid No Yes 2 4 1 1 No Yes No Yes 1 2

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