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Chapter 10

Chapter 10. Meiosis and Sexual Reproduction. Sexual reproduction. Genes—sequences of DNA in chromosome All genes the same = clone, twins. Sexual reproduction. Meiosis Gamete formation Fertilization. Sexual reproduction. Allele—different forms of the same gene

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Chapter 10

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  1. Chapter 10 Meiosis and Sexual Reproduction

  2. Sexual reproduction • Genes—sequences of DNA in chromosome • All genes the same = clone, twins

  3. Sexual reproduction • Meiosis • Gamete formation • Fertilization

  4. Sexual reproduction • Allele—different forms of the same gene • Affects different traits— “dimple”, “no-dimple” • Mixing alleles results in variations of traits

  5. Chromosomes • Chromosome number—sum total of chromosomes • Diploid number—number of chromosomes when including pairs, “2n” • Homologous chromosomes—each chromosome in a matched pair • Haploid number—half of the normal chromosome number, “n”

  6. Chromosomes • Diploid number = 46 (“2n”) • Haploid number = 23 (“n”) Homologous Chromosomes

  7. Chromosomes • Duplicated during S-phase of Interphase • Divide during anaphase

  8. Mitosis • During interphase, chromosomes double • Cell divides once • Chromatid divides once • Leaves 2n in each daughter cell

  9. meiosis • Almost identical to mitosis • Chromosomes mix • Cells and chromosomes divide TWICE before process ends • Ends with 4 daughter cells, each haploid • Pro-, Meta-, Ana-, Telophase I • Pro-, Meta-, Ana-, Telophase II

  10. Meiosis • Prophase 1 • Homologous chromosomes pair up (Synapsis) • Usually swap segments (crossing over) • Otherwise normal prophase

  11. Meiosis • Metaphase 1 • Spindle fibers attach to centromere of each type of chromosome • Otherwise normal metaphase • Anaphase 1 • Homologous chromosomes separated to each pole of cell • Otherwise normal anaphase • Telophase 1 • Cytokinesis (normal telophase) • Does NOT go to Interphase

  12. Meiosis • Prophase II • New centrioles move to poles of new cells • Metaphase II • Spindle fibers attach to centromeres • Chromosomes line in middle • Anaphase II • Sister chromatids break apart, move to poles • Telophase II • Cytokinesis • Each daughter cell is haploid

  13. Meiosis • Several Good animations w/ narration • Animation w/ narration, same style as mitosis

  14. Mitosis vs. meiosis

  15. Mitosis vs. meiosis • Somatic cells • Grow, replace, repair • 2 daughter cells, 2n • No synapsis • No genetic diversity • One division • Sex cells • Reproduction • 4 daughter cells, n • Frequent synapsis • Great genetic diversity • Two divisions MITOSIS MEIOSIS

  16. Genetic variation • Crossover (Prophase I)—Switches alleles • Homologous Alignments (Metaphase I)

  17. Genetic variation--humans • 8,388,608 combinations of homologous chromosomes • 70,368,744,000,000 possible variations of offspring • Including crossing over-- 4,951,760,200,000,000,000,000,000,000 possible variations!!!!!

  18. Gametes--Plants • MeiosisSporesMitosisGametophytesFertilization

  19. Gametes--animals • Spermatogenesis • Primary spermatocyte (2n=46) 2 secondary spermatocytes (n=23) • 2 secondary spermatocytes  4 spermatids (n) • Spermatids  sperm

  20. Gametes--animals • Oogenesis • Primary oocyte (2n)  1 secondary oocyte (n) & 1 polar body (n) • Happens before female is born!!! • Secondary oocyte (n)  Metaphase II • Stops meiosis II here • Fertilization of metaphase II oocyte  1 ovum & 1 polar body

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